Maybe where its allowed, add links to each book on the various store in your signature? For example:
Buy my novels on Kindle: (link)
Buy them for your iPad: (link)
Or for your Nook: (link)
All others try this: (link to buy the epub version)
I know it probably wouldn't go over too well here, but if you did it on some other site that didn't care or cared less, then maybe you'd get more bites?