Populate selection

I want a number of objects to fill a face selection, and automatically re-position themselves as the selection changes.

I created a hand-animated demonstration of what I want to automate and posted it here: http://www.geoffkornfeld.com/TargetMovement.mov

This demo uses only six objects, but I want to be able to do this automatically with hundreds.

Any ideas how this can be done?

Thank you.

- Geoff