I've never heard of a non-invasive spay, but some vets do perform the operation using only a small incision. This site talks about it: http://www.petsavers.org/articles/Sp...nd_Method.html
WARNING: includes surgery pictures.
I also found this article on CNN. It was published in 1998:http://www.cnn.com/TECH/science/9808...ref=sitesearch
I wasn't able to find any more recent research. I did, however, find this article. I found the last part especially important:http://cats.about.com/cs/spayneuter/...=drugs+have+on
"None of these immunocontraceptive vaccines are expected to be a substitute for surgical spaying of owned female cats. Why? Because they do not stop ovulation, nor the attendant frustrated behavior of female cats in heat. Furthermore, surgical spaying helps prevents ovarian cancer and mammary tumors."