V-Ray RT Render Devices Select setting


After reviewing all the current render settings available, I notice the one that I'm interested in doesn't seem to be there. I hope I just missed it. Could someone give me a hand showing me how to change the V-Ray RT Render Devices Select setting? I even tried changing the VRAY_OPENCL_PLATFORMS environment variable but it won't actually change while the Vray RT renderer is selected. What I'm trying to accomplish is to be able to turn on/off Render Devices before each frame is rendered (pre-render script).

If this can't be done in script directly, does anyone have a workaround suggestion (other than don't do it)?