I like the idea of practicing from a sitting position. I'll have to pass that idea along to my instructor. As for the tight pants situation, I'd go with the traditional locks, breaks, and gouges, but I'd add an element of shock to it as well to use my enemy's instinctual fear response against him. Essentially, I'd use as many face strikes as possible, preferably from the sides and behind, and probably add a warlike kiai to that for emphasis. It may not do much, but as long as the entire combat takes less than 10 seconds, it might him enough pause for you to take him down.
On a related note, the Shotokan master at my school has been confined to a wheelchair for most of his life. He's a really old guy, but that doesn't make him incapable of effectively defending himself.