I know a little late to this thread ! but hope the input can help someone else down the track, when I went to do mine I went to a local shop here that specialises in rolling and bending tube/frame - long story short they filled the square with sand to make sure it didn't collapse and then put it through a series of vertical rollers which progressively bent the tube around, there are a few clips online of people using presses and rollers homejobbed together and then they run the tube back and worth slowly pressing harder until it is 'rolled' round -
Best recommendation - find a local bending shop, a good machine place should be able to recommend someone and it shouldn't be that expensive, the problem is finding someone who can roll it so small and tight, on my build I had the same issue and the local shop couldn't get the curve tight enough so had to cut and shut it anyway :S
ahhh the 'Fun' of DIY projects ...