I used CA solvent once on some CA glued material but I really don't know of any solvent to do epoxy... especially without damaging the acrylic. If you have a spare tube to redo, you might be able to drill it out and just reglue a new tube in. If not keep it in the scrap bin until you can figure another use for it...
If you have the same size drill bit and it's old (or if you have transfer punches), use the back end of the drill bit to try and knock out the tube, epoxy can be easy to shear if it in just the right way.
You can try to knock out but in the past depending on the coverage you used must likely just drill out the brass if you still need the blank. Question have you turned the blank yet? If so than the bad news is to scrap both the brass and the blank.
Heat is your best bet to get epoxy to let go.
I have had luck (bad luck since I was not trying to do it) get the tube out by running the pen mill in the tube for a while (not the cutting bits, just the pilot shaft). This created enough heat that the tube came spinning out. If you don't have the pilot shaft that matches the tube (ie. you use spacer sleves) you could try using a HF punch or even make a shaft our of solid wood that should heat up pretty good.
I`m Not sure this would be good for the blank,but heat is used to remove the shaft from a golf club which are epoxied in the club head. Just a thought.
I come up and accomplished getting the tubes out w/o damaging the acrylic. I was trying to figure out how to get heat inside the tube without getting to the acrylic. I decided istead the the melting point of the acrylic would be less than the boiling point of water so I boiled them and the tubes came out with a little work. I put them one at a time in warm water and then brought it to a boil for about 3-4 min. and then with a little effort pushed the tube out. Ill have to see if the acrylic is still turnable or not. I'm a little worried that it may have made the acrylic a little brittle. Will report back on that later.