Hi NJ:
That's a good question! There's a choice on the EFFECTS menu called STEREO PAN with an adjustment for LEFT-CENTER-RIGHT, but there's no description of its (intended) operation in the HELP file. In playing around with it, I cannot get it to do what you want it to do. But, I'm not saying it doesn't work properly -- I'm just saying I can't figure out what it does.
Maybe one of the WAVEPAD grownups can help out with this one.
Jerry
EDIT (20 minutes later; $20 poorer): If you get impatient waiting, I found one that does exactly what you want -- and I didn't even have to consult the help file to figure out how to do it:
http://www.acoustic-labs.com/index.html
They have a trial version that you can play with, but you can't save any of your changes until you buy it. (It won't work at all on Win95.)
Jerry