OK, I see what you are doing. If that's the amount of spoiler travel that you intend to have in the air, I wouln't be surprised if you didn't see a difference. That's a small amount. You would probably see more effect when the flaps are down.

Being that the spoilers are inboard and don't move very much, it should be no big deal. You could start there and increase the mix ratio for aileron-> spoiler and see the difference.

I have used spoilers berfore, but not for roll control.

BTW - Mike: On your Henzil Browne page, the first slat sketch was actually drawn and posted by me