[css3-transitions] transitioning to/from auto value

I was attempting to use transitions in a project last week, and found it very limiting that I could not transition from "auto". I wanted to do a vertical wipe on a list by transitioning its 'height' (with 'overflow:hidden' on the list), but it didn't work well because it didn't start with a fixed height. I could not use percentage, because this was a absolutely positioned OL inside a much shorter, fixed height container.

I also tried using 'clip:rect()', but this was not transitionable at all for some reason (why? I see now that it is not on the list, but I don't know why not). Anyway, I would have had the same problem with that, due to the screwiness of the 'clip' property needing a width and height instead of just four offsets. 

I ended up transitioning from and to a negative margin on the first LI of the hidden overflow OL, but this had other negative side effects that I had to work around.

So, I'd like to propose that a way be found to have to set up a transition to and from 'auto' or intrinsic lengths.  Is this patently impossible because we are setting up the transition prior to getting the used value? Or is there some way it could happen at a late enough stage to know what the actual height would be?

Also, can we add 'clip:rect()' to the list of things that can be animated?