If you go the just swapping the rears, remember that directional tires are swapped different from the non-directional tires.

Click For Full-Size Image.
I solved the same issue by installing the same straight metal valve stems on all wheels, and then used
Milton Industries, air through, screw on 1-1/4 inch, valve extensions on just the rears. Easy to transfer from wheel to wheel.
Easy to air up with a Milton S-693-12 1/4" FNPT Extended Reach Dual Head Air Chuck (available on amazon)

Click For Full-Size Image.
If you like the
135 degree curved valve stem, amazon has them as a screw on extension version to a standard valve stem. Search =
milton industries valve extension to see others.