To those of you who have suggested sleeving the vac pipe in sched 40 or 80, I've thought about this too and agree that it would be difficult but could probably be done.  I haven't gone as far as mocking anything up, but maybe that's worth a couple hours to glue up some pipe and see what the issues will be.

I know adapters are available to convert from 2" schedule 40 plumbing pipe to central vac pipe so maybe that's all that is really needed as a solution for the pipe.

I could use schedule 40 through the slab and footings and then use the adapter to convert down to central vac pipe at sweeps into the inlets.