It probably would physically "spoke up" to the hub, but why would you want to do that ??
• The narrower rim is going to change the cross-section shape of the tire at the road surface in a negative way, which will have a negative effect on the handling. You'd really want to go wider, not narrower.
• You'll also end up with a smaller tire patch in the rear making wet weather riding more dangerous, and tire life shorter.
• Then on top of all that, you're probably considering a 19" front, so you'd need to special order spokes from someone like Buchanan's, and the price of the spokes alone will be equal to the price of a good used rim, which I assume you were trying to avoid purchasing. So you wouldn't really save any money. In fact, when you factor in the labor of lacing the rim you could loose "big time" when you discover the error of your ways and need to get it laced twice.
I can't imagine why you would want to head that direction with all the used rims and whole wheels out there gathering dust. Heck, in the AirBazar right now is a set of Lester mag wheels for $350. Considering that those represent the Optimal Solution for any R75, the path you seem to be considering is much more expensive.