Adding PIDKEY to registry during deployment

Hi!

Does anyone know how to add the PIDKEY to a registry value during deployment? I'm trying to create an installation program for a C# project, and I can get it to do everything but that. (I seem to be able to create my own registry key/value pairs, but I can't find anything to tell me how to take the user-entered serial number and use that as a value.)

I'm hoping this is a really stupid question and is easy to answer :) Or maybe Microsoft's Setup and Deploy options are really so limited, it can't be done (or is insanely difficult).

Thanks!