Well, I don't know how strong bonding the blank is made off so, I would consider and protect/strengthen that blank the best way I can before I cart twisting, bashing, pulling, pushing, etc. so, I would use medium CA and some masking tape to created a solid wrap around the blank, spread some medium CA at half of the blanks and wrap a couple of layers with the masking tape, repeat the process on the other half, use thin CA to coat the whole tape surface to create a hard, stable protecting cover to that blank.
Now, is my believe that, the plastic melted inside the drill bit flutes, bonding with the inside of the blank so, based on that believe, heat is the way to reverse the process so, when the CA on the tape of the blank is dry/set, put it in a vice making sure the blanks top is level with the vice jaws, (this is when a aluminium angle set of jaw covers would be handy...!).
Use a vice clamp and attach it to the top end of the drill bit, make it quite firm grip (use some masking tape on the drill bit to protect it), now you need a small torch flame to heat the drill bit as close as possible to the blank but not touching it.
Allow the colour of the hot drill bit to go red and downwards, keep one hand on the clamp vice and put a slight pressure on it in the reverse orientation, don't force it but maintain some pressure so that, as soon as the heat spreads to the bit area that is stuck, the plastic will soften/melt and you can put the torch away and quickly (before the heat starts to dissipate) , continue untwisting the drill bit until is all out.
Heat and a steel brush will remove ant melted plastic from the drill bit, as for the blank, the end close to the torch my be a little burl but not spoiling it, you will need to re-drill it so, make sure the bit you are using is sharp, go slow and remove bit before it get hot inside the blank, keep all the wrapping on that blank, it is the only thing you have to maintain its structure integrity, it will come out when you start turning it.
It wouldn't hurt to soak the drilled hole with this CA, let dry, re-drill to clean up for the tube to fit.
After the blanks went from square to round, stop the lathe and inspect the blank, with some magnification if available, to give you some piece of mind, put a layer thin CA all over the blank, it there is a minor separation somewhere, you will notice the CA to disappear into that small crack(s), in that case, pour some more thin CA until it absorbs no more, spray some accelerator on it or, let it harden or use a hair drier/heat gun to accelerate the drying process and, continue on...!
This is what I would do if I wanted to save the blanks or avoid unnecessary damage to it...!
Good luck,
Cheers
George
A little more controlled heat sounds reasonable.