In regards to the glider issue, to me the most natural behavior would be for the gliding to begin at the peak of the jump.
Climbers jumping away from the wall: I don't see any compelling reason not to allow this, and jumping is an option you'd have in real-life climbing if you can't reach the next hold. Generally you wouldn't be jumping away from the thing you're trying to climb, but really, my main point is that it doesn't seem physically unreasonable to allow this behavior, and I think it could create some interesting interactions.
Assigning a shimmier shouldn't cause a double jump, but if the lemming manages to touch the ceiling I don't see a problem with allowing it to transition to shimmier. The cleanest way I can think of to do this, as a failed assignment would do literally nothing except consume the skill, would be to require the skill to be assigned on the frame the jumper makes contact with the ceiling, and make it subject to the normal invalid skill assignment buffering rules (e.g. if you attempt to assign a builder to a faller, it will begin building once it touches the ground assuming it doesn't splat). As far as I'm aware, the buffering lasts indefinitely (I don't think it should, but that's another issue), but if it doesn't, or if this behavior is changed, the shimmier-assigned-to-jumper should be a special case where the shimmier assignment will be guaranteed to be buffered through the full duration of the jump.