I'm in the same boat.
I bought a DFGT on GT5 release day.
At first, I started out with a TV tray from Wal-Mart.
BIG mistake.
It was so light and unstable that it lasted about a day.
Then I tried to use one of my end tables.
Even though it's hefty and substantial, even that doesn't work.
After a few weeks or so, I weakened the legs.
(Beyond that, it's not the right height so it's not very comfortable to use for an extended period of time.)
I've tightened the legs back up, and I'll use the set-up on occasion, but I've actually regressed to using a DS3 to drive.
The best choices are either building something custom, or making the serious investment into a dedicated wheel stand.
(Me thinks "building something custom" will be the route I go.)
Peace...