Yes it has been done. Personally I would stay away as it does weaken the ptu case and they can crack without the modded drain as it is..
Drain, Fill. Drive. Drain. Fill and drive. Best way.
Suck the oil out through the Fill plug.
I extended my PTU breather hose and filled the PTU through that. Warmed up the oil so it flows easily. Leave the top fill plug open til it drains out there then you know its full.
Videos are on Youtube on how to suck it out.