I know this might be too late considering the last patch dropped, but to me it does seem like a pretty simple idea that can easily be slipped in that would gave Sappers a bit more use with the game.
The act itself would be simple, with the hammer out a Sapper approaches a enemy cannon and holding down F and waiting for the bar to fill up for around 6 seconds (imagine him/her/it driving a nail into the touch hole) and blocks the artillery for temporary usage.
Have this little act cost either something like 5 or 10 build points or limit it to once a life for balance reasons?
This can easily be undone by a friendly sapper the same way, or just undone by one of the Artillery crew. Maybe even make it a server side option if it is too hardcore for pubbie play?
Thoughts?