Two thoughts here. 1) would using a shorter plug help in your clearance issue? I am using one due to my frame being a 24" Mtn bike. 2) have you thought of using a different style tank? I don't know your level of mechanics, but Rockenstein has a post here in the forum about an apple juice tank....
Silver Bear makes his own tanks too. I have even tried my hand at it and didn't do that bad. Sorry no pics.
With creating/buying a tank you then have the opportunity to mount it elsewhere on the bike therefore eliminating that fear. I know I would feel a lot better.
If you have any more question let us know that's why we are here.
Post some pics. it will give us a better idea of what problems you are facing.