I tried out an idea for bending exhaust tubing with a pipe bender. I filled the tube with hardwood dowel pieces with a 1/4" hole drilled through them. The wood support prevents crushing the pipe. I got a little over aggressive and got a couple of kinks but nothing that looks like it would restrict exhaust flow.
The wooden dowel can be easily burned by injecting some compressed air and heating a section of pipe until the wood ignites. As soon as each piece looses a little diameter, they pop right out.