Ok, sounds like a bit of inpatients here. I would clean the cage ever week, Saturday is always a good snake cleaning day.
Just let the rosies sit in the dish. I use a clear bowl in my cage. I have even gotten my w/c to eat thawed pinks from me. I have to swish it in the water to get its attention. But he gobbles them up with ease.
Let you guy go for a few days. keep an eye on the fish to see if any are missing. Your snake will feed just give it time. Mine has refused for me as well. So this is normal, so don't worry or fret. If your snake looks to be loosing weight well then there may need to see some action done here.
Also listen to Jodu.. she has some really nice Garters herself. Just take a look at Roy Munson's Gretchen thread, she produced that baby.