Please, aby thoughts??
Yes, Sean (and welcome to the Thorn Cycling Forum!):
I believe you might indeed get away with fitting a 700C wheel in place of the fat-tired 26in so long as:
1) Disc brakes were used (as you have mentioned...)
...and...
2) The tires on the 700C wheels were very skinny.
Twenty-niners are bikes that run very fat tires on 700C rims. I don't believe there is sufficient clearance beneath the Sterling's fork crown or seatstay bridge to clear a 700C wheel *with* fat tire.
I may well be wrong, but I should think clearances could be pretty tight.
Is there any way you could borrow one or two of your mate's wheels for a moment to try while the bike is in the stand? That would definitively answer your question with no harm to either bike or wheelset.
All the best,
Dan.