Yeah, turn or grind the top of the tap square to a round section and then drill the end of a steel rod same diam as the tap shank to fit it...........silver solder the tap into the rod end to make a long tap.......BTDT.
Tig welding the rod directly to the tap without turning it down would also be an option......BTDT too.......done that with drills as well......must be concentric.
Ian.