What I did with my 2 cards is the following...
I used the PCI-E power cables to "retain" the cards.
so I ties the cable in a way that they hold the cards at a certain height...
It's not the best thing, but it works...
also, MSI now adds a "retaining" bracket that goes on the edge of the cards...
The HAWK and the new GTX560 (non-ti) TFII has it...
I asked MSI ALEX for the chance to get some and he crapped on me...He said it wasn't needed LOL...I replied, why then the new GTX560 comes with it...I guess they don't want to be involved with it...
But MSI definitely ships new cards with a edge bracket to straighten out the cards....so THEY KNOW.......