The only method to add templates to active listings is to use eBay's Revise listing editor to replace the HTML code in the description section with code you've created from a Saved Listing at Auctiva. It ain't pretty, but with Seven Dwarfs to assist, it's do-able.

I think using Import of Closed listings is still probably a better method. At least with that method you've got the listings stored at Auctiva for later updates and submissions.
Danno