Help please
ATF Fluid change – E53 3.0 litre Petrol

I’m hoping someone has prior experience in solving this problem
I was attempting to change my ATF and accidentally rounded-off the head of the Fill Plug.

I have tried all methods / solutions I could find on-line.
Do not have a welder or access to one, or I would simply weld another larger nut onto the existing Fill Plug.

I used a Universal pipe Wrench / Quick Snap-N-Grip Spanner which has easy access and excellent grip IF TIGHTENING the plug – but those clever engineers did not allow access when loosening the plug.

FYI – I started this removal with an extremely snug open ended spanner, but I was not aware that hit the outer flange of the sump which forced the tool to move away from the plug, which started the rounding-off. Then I tried the extremely snug closed end of a combination spanner, with the same result.

It ‘appears’ to me that I would have easy access with the Universal pipe wrench if I removed the sump, but I do not have facility to leave the car for extended time if that does not work.
Any suggestions would be greatly appreciated. The only method I have not used is a blow-torch, and the welder as noted.

Thanks, Sal

PS – big thank you to ‘championscooter’ for his post – particularly the wooden ramps suggestion, which gave me supreme confidence when working under the car