The client has a GPU-related feature we added a while ago
(> 1 year) but for some reason never documented.
In combination with the anonymous platform mechanism,
it lets you use GPUs not otherwise used by BOINC.

In your cc_config.xml you can specify a GPU that's not used by BOINC -
either a vendor that the client doesn't know about,
or a GPU that the client knows about but decides not to use
because it's less powerful than another one.
The entry looks like this:

<coproc>
<type>some_name</type>
<count>1</count>
<device_nums>0 2</device_nums>
</coproc>

The name (some_name) should be something different from
the names used by BOINC (NVIDIA, ATI, intel_gpu).

In your app_info.xml file, you can list an app version that
will use this GPU.
It should include a <coproc> element using the same name.

For example, if you have several different NVIDIA GPUs in 1 system,
you could have a separate <coproc> element for each one in cc_config.xml,
and specify the apps that can run on each on
in your various app_info.xml files.

This is documented here:
http://boinc.berkeley.edu/wiki/Client_configuration#Options

Let me know if any questions or problems.

-- David