I tried your technique today Blake.
My V-tool is a brass job, lubed up with beeswax.
http://www.digzo.com/images/3ab/DSCF1154.jpg
Using 34mm tube, I kept getting devit either side of the notch. Maybe I was working it for too long.
I also found it difficult to rotate a large tube in this hand and a small tube in that hand. Well not difficult, I mean it was difficult to keep the smaller tube on centre and make a good weld.
Reason being both ends are open so I can't blow in to perfect the weld.
Sounds like a good way to work though and I can see where you're coming from.