Or you might get lucky and find the right chain stay/chainring/freewheel combination that requires no chain tensioner. I can't remember what its called or where it is (big help, I know) but there is a website out there somewhere that talks about setting up a vertical-drop SS mountain bike without using a chain tensioner. It's all about getting the getting the chain length perfect. You might be limited to certain chainring/freewheel combinations though.