Initial comment:
There is major work being put into producing this for Joomla 3.2 if not then 3.5.
It has been mostly done but a lot of testing and fixes need to be made
Update:
This feature will be bought out with Joomla 3.2 which is going to be out around 1 months time. The feature will simply allow the admin to add multiple form fields and remove them at ease.
You can test this and possibly help towards debugging it here:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=30781