Well, if you're taking this prize money out of the prize pool created by the buy ins, at the moment the best way to do this, I think, is adding the prize to the list under the "prize" tab. There's an option to allow you to manually assign this prize to a player after the tournament's completed. You can call it whatever you want to and I believe it will show up under the "prize" cell in the display. I'm not completely sure though since I've never added a manual prize before.