I'm kind of in the same boat, my ball python hatchling hasn't eaten since I got him about 2 months ago. He's not a BRB though, so you've got a much better chance. I would give it a least a month until you start getting worried. I don't use live much but I can offer some f/t tips, it helps to try everything if you've done live a lot before.
Something that often helps is braining or at least scenting, my guy used to not eat f/t unless I left them in his cage overnight after being rubbed on a cloth that had been with my rats. You can do the same at a pet store, you do get some funny looks though. You can also brain f/t mice to increase the smell, just cut open the head of a pinky or other very young mouse and smear the liquid around its head. Gross, but attractive to snakes apparently. I also leave them heated overnight in the cage inside a little toilet paper roll tube so it's more secretive. Heating them up enough helps too, heat water until it's almost boiled but not quite and drop the mouse in a baggie in there for 15 minutes, if you aren't already.
If he keeps on not eating, then you can consider force feeding and other less fun options. But you have a lot more time, and luck on your side since usually rainbows are great eaters. Another thing you can do is get a poop sample to the vet if he's still going to the bathroom, put it in a plastic baggy and ask them to test it (although they might make you make an appointment). It might be due to parasites, a bacterial infection, etc. Good luck and keep us updated, I'm sure everyone will be on to tell you their little tricks too.
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Danne
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1.0 '07 BRB "Monroe"
1.0 '08 Pastel BP "Sebastian"
1.1 Leos "Bowser & Peach"
0.3 cats "Beast, Smokey & Thelma"
0.2 Dumbo (non-feeder) rats "Josie & Holly"
0.4.2 fish
Email = dshoback@eden.rutgers.edu