See this link...
http://pages.ebay.com/help/sell/two-categories.html
It looks as if you can do it if you list directly through ebay (not sure, I've never listed on ebay motors)
But I tried to do a test listing on Auctiva and no matter what I did it was either one or the other...couldn't do both. Maybe filing a support request would help. At least they could tell you if it's even possible, since ebay.com and ebay motors are essentially 2 seperate sites.