Mining non-primary GPU

I'm launching ethminer.exe -U --cuda-devices 0 --farm-recheck 100 -S...
keep getting "CUDA error in func 'ethash_cuda_miner::getNumDevices' at line 112 : unknown error."

win7 device manager says my gtx 970 is device 0. When I execute "ethminer.exe --list-devices -U" it gives the same error and crashes.

Monitor is hooked up to integrated graphics. Any ideas?