Is it possible to tell Mach3 to continuously to run a rotating axis at a specified speed?

In some cases, it is useful to be able to use a CNC milling machine as a lathe. I have a three axis CNC router with an additional table with two rotational axles. I would like to be able to tell Mach3 to run the B axis continuously at a high speed and at the same time move the other axles at a low speed. The idea is to use the B axis as the spindle in a lathe.

Is it possible to do this, using G-code, VB commands or some other way?

My milling machine looks like this:
http://www.ebay.com/itm/271434433386

Best regards,
Daniel