How can i tell Blender to use only 2 GPUs out of three ?

I want to tell Blender to use only specific GPUs for CUDA, Card 2 and 3, and use the Card 1 for OpenGL.
But i can only choose 3x780 or each card separately. But not 2 cards (2,3, or etc.)…

The thing is i want to dedicate to render/cuda-preview to the two other and the first GPU ram is heavily used by OpenGL (15 Mio Polys) on the first card so it limits the other two cards on CUDA, also even if they have more ram free (obvious), now that i need the RAM to the limit AND i need realtime CUDA render + full OpenGL. :stuck_out_tongue:

So is there a solution ? I hope yes, but couldn’t find it so far (ok didn’t look too much :-P)… Some startup parameters, config file ? Please don’t tell me i have to compile the option, it would be a nightmare, im in heavy 2K production and depend on the official STABLE build. LOL (Vader: Im your father! Luke: Nooooooooooooooooo…) :stuck_out_tongue:

I am on OSX 10.9.4, Official build (latest)

Sidenote: Please could you make each card selectable with a box, instead of a dropdown menu ?

Many thanks for your help in advance.

EDIT:
>>> bpy.context.user_preferences.system.bl_rna.properties[‘compute_device’].enum_items.keys()
[‘CUDA_0’, ‘CUDA_1’, ‘CUDA_2’, ‘CUDA_MULTI_2’]

This is what i can set on the python console (same thing, each or all three), is there a way to set cuda 1 and 2 as a cuda_multi trough python ?

No, you can’t select in OSX the CUDA cards. The Nvidia Panel only switches things like ECC Memory or between Apples Nvidia Drivers and Nvidias Native Drivers.

But any CUDA program can access any GPU arbitrary, so there should be a blender setting ? Config file ? etc. ?

So, any other idea ?