A co-worker of mine used a piece of pipe the right size and a hammer to make the center holes larger on some hub caps ,to fit over a larger hub --he stood the pipe up on the floor,laid the hub cap over it,eyeballed the "center" and used the ball pein end of the hammer to cut the hub cap,much like you use one to make a gasket out of a sheet of gasket material...it worked pretty well,folded the metal inward and made a lip,with no sharp edges sticking out..
I used a similar method Rene described to use a hole saw to cut larger center holes in a pair of rims..I bolted 3/4" plywood to the lug holes to give the pilot drill on the hole saw something to "center" on...worked slick,but I did toast my old Black & Decker drill in the process!..had to finish them in the drill press,which required taking the tires back off the rims..