ok OpenType sages, I have ran into a speedbump in trying to solve something with random contextual alternates and trying to 'un-random' them at very specific times.

I posted a comment on a previous thread earlier tonight (http://typophile.com/node/19625), but realized it might be best to create a new one (someone slap me if I need to go back to the old one)

My question is: given that mentioned randomization approaches with the calt feature, what happens if I want to ignore certain letter combinations in lieu of something more specific to the typeface in order to avoid pairing a one and two story 'a' together or a standard or binocular 'g' together for instance?

I only want to 'control' this pairing if the letters are next to each other?

how can I correctly ignore a pairing but keep the rest of the randomization intact?