This is something I never have to do on our parts (the holes in those are small and long) but I can see that it would be very useful for machining those bigger holes. Have you tried doing it as a Profile job and setting the technology as Roughing and cearing an offset, perhaps with the cutting set to troichoidal. There is also a setting on that page for making the cutter complete a Z level before moving on to the next.
Another way of doing it would be to work out the logic for an approximation of a spiral and then putting that in the post as a drill job. I saw something like that some years ago in a different life but it would be a bit a job though.