I did the same as Matt above. I used small square tube with pieces of angle on the ends to bolt to door frame.
You could glass a piece of flat stock in that area, and do the same. Here is a link to my build log:

http://www.clubhotrod.com/hot-rod-bu...del-coupe.html

Look at posts 115, 122, 123, 215, and 221 for some pics of mine.

Good luck, Rich