I have this idea of installing a push/pull switch into my Ibanez S by a local tech, and I'm wondering how it would reflect on a humbucker-single-humbucker pickup configuration... opinions?

To me whether to do that really depends on what type of sound you're hoping to get from coil-tapped pick-ups on your S. I had an S for several years, and my short response is that you won't get close to the Fender-type 1-2 and 4-5 positions of a strat. Of course you might not actually be looking to get that type of sound.