can only mine using all GPUS or 1. Cant' use more than one but less than all

[jjziets]

I have 3 GPU's in my system. I want to mine using qtminer with devices 0 and devices 1 not device 2
I noticed that the switch --opengl-device can only be 1 number. Therefore it is not possible to mine using two devices only.

ethminer -G --opengl-devices 0 1