Sorry to say that, but this is the quick and dirty way to do it without any warranty to end up with the wheel centered nor in line with the frame axle and front wheel !
Kinetics has a jig that hold the rear triangle at several points and produce a controlled, reproducible enlargement of the frame that warranty that all enlarged frames are identically enlarged with the same final shape for all tubes.
He of course dismount the rear triangle from the frame before enlarging it.
He posted pictures of this jig on FB.