Hey Mike,
That is an excellent idea! It would solve one of the problems with this style of pen. A lot of them you'll see will be fatter so that there will be more "meat" where there is no brass tube. Fat isn't bad, but this would allow it to be turned much thinner without worry of cracking.
It would also solve another problem, that of the top barrel being a tad loose where it meets with the bottom section. I haven't really had that problem, but it can happen. Angelo turns a little tenon on one side and a recess on the other to insure a secure fit. But using the brass tube should accomplish that just fine.
Thanks!
Scott.