Thought I would post an update to my idea of under dash storage for my Roadster. The photos below are of the second generation - I decided I didn't like my first attempt with the wire basket.
It isn't a shelf per se, but considering the clearance problems with the steering column, GAV rod, fuel valve, and handbrake I came up with this idea. The natural upsweep of the fuel tank at each end seemed to make a natural place to use for some kind of storage. Hobby Lobby had these 7" x 9" plastic baskets for $3.00 each, so I modified them to fit at a slight angle, but they nestled in place fairly nicely and the best part is, I didn't have to drill any holes! Also, no problems entering or exiting - they are up high and out of the way and don't intrude into precious knee and leg room.
Not as snazzy as the shelf I had envisioned, but the baskets offer quite a bit of storage for loose items and they don't look too bad either. I'll admit that wicker, cane, or bamboo baskets would be my preference over plastic, but I'll keep looking for something along those lines while using these.