I've come up with a new way to mold up the thick push tabs that are used to hold side panels in place.
Grab some wet foam from Jo-Ann fabrics:

Cut in half:

Press around a good tab to get the shape:

Tie together with zip ties, pour in favorite plastic (my choice is Duramix 4230)
Cut the ties, remove the mold and you're left with:

I used a nylon brush to clean off most of the leftover foam, then glued it onto the offending panel.

I thought it looked better than my first attempt at building a push tab from the ground up:

The only problem is the cost of the supplies. Duramix is expensive ($55 at my local CarQuest, $40 online shipped), never mind the cost of the applicator gun. But I do have a good working tab now.