China Southern flies CAN-HKG; I don't see why you can't buy 2 tix, one on China Southern and the other on whatever airline you want to fly from.
I'm certainly no China expert but I'm sure that you can get from anywhere in China (basically) to CAN and from CAN to HKG. I also figure that there would be non-stops from WUH and CKG since they're major cities....
I think a long meeting with a TA may be in order to get what you want....
just some thoughts...