Actually even if they are glued, you can still remove the caps, it just takes a bit more work. Soak the ends in nearly boiling water for about 30-45 seconds, and then use a t-pin or small screwdriver, etc, insert into the hole and gently pry up the cap, going in circles. The bigger problem is is you want to remove all of the glue residue inside so you can then use them with a drip tip. It take a bit of scraping, in very tight quarters, plus you don't want the bits of glue to fall down into the filler.
All in all it's better to just fill using the condom method for the glued in cap styles. If you need removable caps it's better to just go ahead and buy them that way, unless you are really pinching pennies to the extreme.
