Let's see:
1. Frantic efforts to avoid real or imagined abandonment.
How about a Venus (relationship, union) or Moon (nurture, protection) in poor condition and especially if menaced by Pluto or Martial influences? Pluto of himself is rejection, abandonment, isolation, "outsider-ness". If Moon-Neptune (fantasy, disattachment from reality) is so posited that the implications reflect solitude, being unwanted, etc., this could qualify. How about some of the things implied by old Saturn? Low self-esteem can lead to feelings of "nobody wants me;" Saturn in the 12th can mean "absence of the father," which in some cases can lead to the same thing.
2. A pattern of unstable and intense interpersonal relationships characterized by alternating between extremes of idealization and devaluation.
Unstable and intense relationships....How would Venus-Uranus do? Can you think of other possible signatures describing this sort of thing? I can.
...extremes of idealization and devaluation....Neptune (for example, square Saturn). Dual signs. Emphasis on Libra (famous for fence-sitting). The Moon (all things tidal in nature...ups and downs, comings and goings) in bad condition and perhaps in hard aspect to Venus (values and ideals; what we appreciate or are repulsed by.) Mercury is ambiguous, and in the right sign/house or right aspect might show something along these lines. This ambiguous view of relationships (or the people involved in them) probably spills over into all of life -- so any position/aspect that shows this sort of ambiguous, dichotomous character would contribute to the condition.
3. Identity disturbance. Afflictions to Ascendant, its ruler, Sun or Moon. Moon or Neptune at the Ascendant. Signs of extreme "empathy" (heightened sensitivity to feelings of others, to the point of confusing self/other.....not so uncommon.) Disjunct planets. Lots of other things.
4. Impulsivity. A powerful Mars, afflicted (maybe by Uranus, Venus, Neptune, Moon.........) A strongly emphasized Aries. A strong and unstable Moon. Any symbol of excess, such as a poorly conditioned Jupiter, or indications of unbridled or compulsive appetite. Possibly indications of "childishness", one of whose characteristics is impulsivity.
And so on down the list. One can surely find a half dozen different indicators for each of the 9 criteria. This is why I suggest that the astrologer will be most likely to succeed at diagnosing such conditions by looking for indications of the symptoms -- whatever the astrological indicator may be -- rather than seeking out some single "significator".
Neptune is a good indicator of substance abuse. But there are exceptions.....hmm. So Neptune is not an iron-clad signature. Funny how before Neptune there was the Moon and Venus....and didn't Lilly and his friends mention other planets in regard to "drunkeness" (substance abuse)? Al Biruni associates the 8th House with evil effects of drugs, Mars, Moon, Venus, Saturn all pointed out in cases of drunkeness by the 17th century English astrologers. But these planets indicate such a condition only if they are determined toward it by afflictions, sign positions and so on.
Therein lies the rub with cookbook signatures.
I guess the symptoms of BPD are the same as the effects. I find that the listed symptoms, by and large, seem more or less "unrelated" as far as their form of expression goes (e.g., "impulsivity" vs. "abandonment"), yet some are related ("suicidal behavior" vs. "feelings of emptiness")...so, some indicators might show more than one of the symptoms, while other symptoms would probably require a separate significator.
I find it interesting (off topic, but...) that most people insist that man has Free Will, and at the same time accept that psychological conditions such as this one (which affects our entire life) are involuntary and beyond our control.
If astrology is not consistently reliable....if it sometimes gets it right, sometimes not....and if the environment plays such a large (and horoscopically undefined) role in creating us, then I question the utility of astrology. Personally, my years of studying charts and people leads me to believe the horoscope does determine our lives -- including the environmental factors (within reasonable degree). If the horoscope fails to accurately portray an individual and his/her life, it is my fault, not the horoscope's.
The relatively simple thing called borderline personality disorder underlines our difficulty as astrologers. Life is long, the human being so extraordinarily complex, and our own understanding so limited..... Heck, the weatherman does well to get the weather right 5 days in advance.