If you're not worried about preserving the fake can for anything, as I was, it's easy to remove. If you examine the tube closely, you'll see a spot right over the 3-lug mount that looks like a little round spot that's been filled or spot-welded over. I used a dremel tool with a grinding wheel to grind down the metal tube and spot weld material until the top of the steel drift pin was exposed.
I put the tube (the whole receiver actually) in a drillpress vice and drilled out the spot weld area with a small bit (start small, working up in size). You can skip this step if you grind enough material down from the tube to fully exposed the drift pin.
Once the pin is exposed, I clamped the fake can tube in the vice (again, don't expect to "save" it for anything using this method) and sprayed a bunch of WD40 into the end where the 3-lug is inserted. Holding the receiver of the gun, I rotated the entire barrel/upper clockwise, CCW, in tiny movements. The aluminum tube is soft, so the steel drift pin will distort the hole in the tube, as you twist the tube back-and-forth.
It won't take much of this, and the hole will be distorted enough that you can turn the tube upside down and the pin will fall out on its own. You'll have to put the tube back in the vice and twist some more to pull it the rest of the way off of the end of the barrel (mine was a really tight fit, hence the WD40).
When the tube comes off, there's no paint on the 3-lug or end of the barrel, so you'll need to paint that or leave it in the bare metal. I used hi-temp engine paint to finish mine. There'll still be a small hole/indention in one of the 3-lug's lugs where the drift pin was. Some people will this with JB Weld, etc. and that's an option you may want to do, as well. Good luck!