Depending on the OS version you may be able to do this:
1. Find out the exact screen name. PPaint screen grab may help.
2. Config the mui screen handler thingy (strait down mui:) with a screen with the same name.
3. Write a script that opens the screen (like: muiwhatever open Windows) then start PC Task and finally closes the window again (!). Hint: check that mui things arguments in a shell window.
If this doesn't work and PC-Task still opens a new window then you have no options than to dig into the aminet swamp and try finding a screen promotion utility.
Unfortunately stuff like this sometimes is only found bundled with unrelated archives; in this case a graphics driver archive or an RTG archive would be the best bet.
