caulking in extremely tight area

So I'm trying to 'get my air-tight on' and it's requiring me to caulk in a very tight area (basically where the roof and the walls meet). I need some sort of "caulk-extender" (and believe me the double "entendre-ness" of this post is not lost on me) that will allow me to put caulk in that corner. I did a quick search and came up with nothing. Anyone run into this before? Thanks.

A length of rubber tubing on the end of the caulk tube, maybe with a reinforcement wire taped to the tubing to keep it rigid might work.