i may take a crack at this tomorrow. need like an expansion bolt with rollers on the end of a flexible cable... but its such a small hole as dddd says- I cant imagine anything that could fit through and then be robust enough to do the job.

there are two sides: perhaps something from one side that blocks and the other side that expands when it hits the block? not sure but I see potential being able to go at it from both sides to increase the total mass one can get inside the tube to do the job.