Towing Issues: How to best remove a 19 mm lug nut which has the corners rounded off, vise grip pliers, buick skylark

Question
'86 Buick Skylark:
How to best remove a 19 mm lug nut which has the corners rounded off.The other lug nuts came off easily,but only this has no “top” or “cap” & probably allowed rust to form in the center where it  contacts the bolt .

I've used Liquid Wrench & some pounding & a pipe as an extender  bar for  an x-shaped or “cross” lug wrench.

And I will probably use more Liquid Wrench &
maybe some pounding with a hammer & chisel-Good Idea?.

The real problem is finding something to grip the lug nut.

I could also pound a smaller socket on to the nut --18 mm being next smallest  & 11/16 smaller still--and try to use a  ½ inch drive 140 lb Torque wrench.

I don't have a breaker bar or impact wrench,but do have pipes of various sizes.

One last question : I think if I put all the other lug nuts back on it would take some
pressure off the Difficult lug nut-Do you think?  

Also I wonder : Does the position of the lug nut, say 6 o'clock or 12 o'clock on the wheel,
matter pressure-wise [especially if it's the last remaining one?] --because I could turn the wheel if it would help.  

Answer
Your local auto parts store should have a special socket which is tapered on the inside with a gripping surface and can be hammered onto the rounded nut, somewhat like driving a smaller socket on.  I've never had to use one but I heard that they work.  

If the lug nut sticks out far enough a monkey wrench or large pair of vise grip pliers could also do the trick.

Putting the other lugs back on to take pressure off could help a little but is not a major contributor to the lug nut not loosening.

Good luck.