I also had oral tongue cancer, and am happy to say I was able to go through treatment without getting the PEG tube. I lost over half of my tongue during surgery, had reconstruction, and finished my treatment on 1/13/12.
I will say, however, it was very difficult to eat during treatment, and continues to be a challenge. By week 2, my ulcers were very bad and I switched to a mainly liquid diet (ensure plus). During treatment, I managed to keep my weight stable, and only lost about 4 lbs. my main motive to stay off the feeding tube was that I didn't want to have swallowing difficulty after, so I tried very hard to maintain my nutrition and hydration.
Unfortunately, it was not easy, and still challenging to eat! I am still getting ulcers, but have begun to eat solid food, and hope the ulcers will end soon. It gets better though, and it is definitely possible. Good luck!