I have not experienced this, but I haven't messed with my Extendar that much. A possible quick-fix could be something like putting a square (or multiple squares, as needed) of scotch tape over the peg before connecting him. That will effectively make it "thicker" when sliding into the hole. If nothing else, it only takes a minute or so to figure out whether or not it works, and worst case, you're out a few tiny pieces of tape.
Bits of paper towel are also an option. It kind of depends on what will actually fit in there.