FAH puts blocks in place to prevent tricks to protect the accuracy and validity of the science.
The FAH client does hardware detection, so no luck faking that either.
And no setting options if running V7.
If you run a V6 client, you could try the "-forcegpu nvidia_g80_1.0" flag. It's a little know flag to get work units that don't support the latest compute version (1.1). Normally, you would use "-forcegpu nvidia_g80"
And I have no idea if they accept that setting any more (no WUs available for download), but worth a shot.
Of course, if this works, it only lasts until the core_11 WUs run out. It went end of life as previously announced on the FAH news blog.
So plan for an eventual GPU upgrade to keep folding...