This is exactly what I'd do. Edit the G-Code as a copy and use M04 for spindle start, rerun the program (if your machine supports it). I've done this a couple of times myself.
Oh, and been there done that with PVC/HDPE. Two things:
1) Upcut bit, get one
2) Option to use a perimeter pocket of say 3/8 and use a 1/8 bit, this gives a little space for the swarf to get picked up by the dust collector