Actually, I like the new channels better. What we need is a way to destroy down ramps from the upper level (in addition to the current destroy up ramps tool).
Seems like the essence of the problem to me.
One way might be to allow for a trigger to be attached to a constructed ramp. When triggered it could either collapse the ramp into nothingness like a support, or allow for it to move up and down like a flood gate.
By replacing one natural ramp along a trench with a constructed ramp and hooking it up to a trigger, you could safely remove all the remaining natural ramps, let the miner escape, then rid yourself of the final constructed ramp.
It would require more time and effort to set up, and probably would work poorly for 1x1 pits, but it would be a start. There might be some other uses for ramps that can be made to appear and disappear by trigger. Mechanically, it seems about as technologically advanced as a flood gate.