I used short-haul rewards (12K) for a YYZ-ORD, purchasing an ORD-SIN ticket from UA.

A few issues:

1) availability now that KK is gone.
2) 15K points, unless you get a reward sale
3) No guaranteed protection if your YYZ-ORD leg is delayed/cancelled.

That said, it worked for me, as the 12K was more than covered in the 21K for ORD-SIN.

NV