A Line drawn call back may be neater than my current attempt - I've been playing with this in a local branch - just adding segments when the turtle is moved if the pen is down.
However-  a few gotcha's here:
* Lots of line segments are bad
* Trapped bouncing turtles will eventually miss a collision and break the simulation
* Lines are drawn as a turtle moves- which creates lots of tiny lines - especially at the top of a bounce curve.

This does still sound kind of cool - but at a first shot it is a lot harder in principle. 
Perhaps I can push the branch - you can play with it and see what I got.