I've done that as well, but the pilot bit always seems to wander
One guy claimed to have welded a hole saw to a piece of 2" pipe, allowing for a better alignment. Maybe. Be interesting to see how he kept it sharp - my hole saws seem to survive but ONE encounter with the gravel on shingles ... and I'm still looking for an easy way to get the tar off them!
Now ... I just might ask a machine shop to bore a piece of 2 1/2" aluminum round to fit over a hole saw extension.
