one of those reverse screw things might do the trick. "easy out" i belive they are called. ive had success with them once.
how big is it? oil temp sensor woudl be fairly large right? how did you snap it?
how tight is it in there?
and how deep is it?
if you can get access to it, you might be able to put the item in a vice, and slowly tap the bolt on the edge. spinning it out bit by bit. use something sharp and a small hammer.