I've had the same problem, and did a lot of research on this.

In the end I found this solution, which I think is by far the slickest out there.

http://bjorkoy.com/past/2007/4/8/the...st_way_to_png/

Its very inobtrusive and manageable, as seems to work perfectly.

PS - its going to be incorporated into the new TF design to cope with shadows etc.