Trumpy, an EMT bender, or the correct size EMT bending shoes shouldn't deform the EMT so no inside support is needed.
When we bend PVC (RNC) here we use heat to soften it. This can be from a heat blanket that wraps around the pipe or a hot box (oven). Since the conduit whn properly heated is as soft as a rubber hose the larger sizes- 1-1/4" and above require support. I have always used compressed air. We have end plugs for each size, one of each has a connection for an air line. We connect this to a tank of compressed air fitted with an adjustable pressure regulator. Around 6psi will keep the conduit nice and round.
-Hal
