to make things a little more complicated: I got the same problem, but I'm using the Benq FP931 as a second monitor in a dual-head (Xinerama) setup.
Everything is working fine except for that damned black stripe on the Benq monitor...
I have tried the solution suggested above and it works fine for the Benq, but then (without the use of EDID) the resolution of my main monitor drops to 640x480.
I think the problem appears because I'm using the same graphics card for both monitors (DVI + VGA) so that EDID is disabled globally, and not only for the Benq. Adding modelines for the primary monitor does not help either, the always remains 640x480.
Any ideas or help would be greatly appreciated...