I use Methyl Ethyl Keytone (MEK) and clean white styrofoam. Dissolve the styrofoam until the MEK can take no more - the dissolving process takes longer and longer, then has little effect.
The solution is a bit thick so I often add a bit more MEK and then place my pre-drilled blanks into the solution, weigh the blanks down to make sure the entire blank is covered.
Then either you can vacuum, or use pressure, or just let it soak for a few days.
Remove the blank and let the MEK flash off - pretty quick I might add.
Re-drill the hole to accept the tubes, mount on lathe and turn.
BE CAREFUL OF THE MEK ... the liquid and the vapors generated are deadly over time. Use the solution in a VERY WELL ventilated area and avoid skin contact with the MEK as it is quite easily absorbed into the flesh of us mortals.
BTW, do not mix dark woods with lighter woods as the MEK will remove some of the surface resins of the dark wood and cause any lighter wood to be come dyed a bit.
Good luck if you try this method...