Sorry to hear about your surgery, and hoping you're doing OK.
Given that you have no machinery, and a proper broach could prove to be quite expensive, and you have no arbor press with which to push it, here's an idea that may work, and easily. If you have an air chisel, alter the end such that it will slide along the desired surface so it will cut flush with the contact side of the chisel, much like a gasket scraper. If you can get it started in the right location, the load of the flash against the chisel might keep it running smoothly along the inside surface such that it will cut flush. Manipulating the angle of the chisel in the tubing would help. Unless the flash is extreme, I can't imagine it trapping the chisel such that you couldn't cut at least half way from each end of the 4" section of tubing you described earlier. Again, the amount of flash is critical. Too little and it won't work at all.
Good luck, keep us posted.