Interesting that you should bring this up. In my Judo training I have recently started forcing myself to avoid using my opponents gi for gripping. I have also started grabbing the obi(belt) more. Right now I have been using Uchi Mata, Osoto Gari and Tai Otoshi. I can do Kosoto Gari like that but it is more for training that practical Sumo application.
There is another thread I posted on my experiences at the U.S. Sumo Open. I strongly recommend that you read through it as I think you might come across the same problems.
In the meantime, where are you located. I may be able to refer you to someone in your area.
Also, please put your real name in your posts (E-budo rules, you know. Besides, it's good courtesy.)
There is a Texas Sumo Yahoo group and an American Sumo Yahoo group. If you are interestede shoot me an e-mail at yodel@texas.net.
Take care,
John Hidalgo
If there is anything I can do to help, please feel free to ask.