Hi Ray,
Unfortunately, that is not a possibility because the Auctiva store is directly linked from your eBay auctions, so it is against eBay regulations to offer anything for sale outside of eBay on that page.
However, when we intruduce out inventory tools, which will be part of our Phase II release, which is tentatively scheduled for Q1 of 2007, we will be incorporating a feature to upsell items related to the one(s) being purchased on the Auctiva Checkout page.
-Mike