I don't know if it'll work for you but it did for my friend, He had a tiny terrier and then got a biggg lab. the tiny terrier(terror) didn't like the biggg lab so Geoff smeared cream cheese on each dogs back and they licked it off of each other-now they are the best of friends. Hopefully your beasties don't fight over food!
Good luck!!!
Also, Foxgal love the pic of the biggy and the teensy