Art,
Like Stuart said, you could use an arduino. Personally I never liked the idea of adding an arduino to a cnc machine, it never seemed like it would be robust to me, I add PLCs to our machines instead. But that is my opinion.
I'm not sure about drilling while it is machining a profile, doesn't sound like a good idea to me. But I also don't know your setup and it may be working just fine for you.
If you use a servo in Mach4 you can write a macro to drill what you want using DROs on the screen to set start, end, and rest positions.
Have DROs for:
Drill Start Position (DSP)
Drill End Position (DEP)
Drill Rest Position (DRS)
Drill Feed Rate (DFR)
Your macro can rapid to DSP DRO value then drill to DRE DRO Value at the DFR DRO Value rapid out to DRS DRO Value.
If you use an OBO Axis you can still monitor axis position. I figured out how to do that a few months ago.
The only thing you would need to figure out is how to do it while the machine is running your turning operations.
Just spitballing here.
Write a function to do the drilling ops and call it from the PLC script. That may allow it to run in the background. This is just a theory and I don't have time to delve into it this week, we are heading to IMTS in the morning so I won't be able to test this.
Maybe Craig or Steve can jump in here and see if this is a feasible idea.