
There's no problem in doing so if you are having someone else stackking the dog in the line up. Myself or my Dad have done this when only one of us can go to a show, plus mum, Mum stands the dog but we show it. Just confuses the judges sometimes so make sure dogs stay in correct order. I have also done this when showing my own dog but someone else wants me to handle their dog aswell.
Also in the YKC stakes it's very popular for those juniors having two dogs which they enter and get a friend to help them out but the owner has to show it.
You should remember though, although no rules against handling the two dogs, you should be displaying the correct number fo the dog you are showing. Therefore when running the 2nd dog you should change ring numbers. I however have never done this but it's something to bear in mind shoudl you feel anyone might get picky.