Changing priority of stubborn process

I've got some processes (mcshield.exe and scan32.exe--Part of McAfee
VirusScan Enterprise) whose processes refuse to be re-prioritized
through the task manager. (These processes are spawned by the "McAfee
Framework Service" service, I think.)

These are not the only offensive processes, but I'm using these as a
(particularly offensive) example.

Is there a way to reprioritize these processes, and/or other stubborn
processes in general? I don't mind if mcshield runs, but when it runs
at high priority (which it does), my foreground apps are useless.

My first thought at a solution would be to try re-defining the service
so that instead of running:
"C:\Program Files\Network Associates\Common
Framework\FrameworkService.exe" /ServiceStart
.....it would run:
"C:\Program Files\Network Associates\Common
Framework\FrameworkService.exe" /ServiceStart /low

....but I don't know if a.) It's a good idea b.) that it would work, or
c.) how even to do it.

I would appreciate any temporary or (preferably) permanent solutions.

Thanks,
Jamie