A press fit, or shrink fit is not permanent. You can always heat the Outside part while cooling the inside one to separate the two. I don't know if ATF would approve this next method, but it would be impossible to remove without machining and no significant heat required to install:
Machine the two parts with a slight interference fit---a true press fit (~0.0002"). Cut matching grooves in the I.D and O.D. Fit a spring washer (much like piston rings used in cars and the AR bolt) that is the same width as the grooves (0.001" clearance). Install the spring on the barrel and compress it when you press the flash hider. The spring washer/piston ring will snap into the matching groove in the hider.
The two will now be impossible to separate without machining off the hider. Heat and refrigeration of the two parts will still not be enough to allow the parts to separate; it will allow the hider to be rotated if needed, however. Note: the shoulders of the grooves and the washer need to have next to no chamfering as a radius or chamfer might allow for shimming the spring washer and allow removal with temperature differential.