http://www.metalsmith.org/edu/equipment/rollers/DavesRngrlr1.jpg
http://www.metalsmith.org/edu/equipment/rollers/DavesRngrlr2.jpg
http://www.metalsmith.org/edu/equipment/rollers/DavesRngrlr3.jpg
http://www.metalsmith.org/edu/equipment/rollers/DavesRngrlr4.jpg
Taking the lead from my homemade roller (remember I didn't make it, but it gives me ideas) you could make or have some enterprising blacksmith make a set of adjustable collars to fit the outside rollers (I don't think collars would be necessary for the pinch roller). These 'collars' could be as simple as a pair of "C" shaped pieces that would bolt/screw together around the rollers.
This is a similar collar that I've taken off an unrelated piece of equipment. This isn't necessarily the form to use for a tire bender, but should give you a starting off place. Hope this helps with the skewing.
Dave Brown
