I have just finished (fingers crossed) with a similar issue mine had eaten some cyprus chips and that is what the vet though caused the issue, substrate wood chips, personally I am not completely convinced of that but... that is what she told me.
I also did the 20 min soak (88ºF) twice a day, the vet gave her a stool softner by tube in her office after taking some x-rays. She had a monster poo and the bloating seems to have gone away now. The other suggestion was a add a small amount of water to the rat (F/T rats not F/K or live) That dehydration can cause issues too. Mine never stopped peeing just poop and she was having fairly wet pee so dehydration wasn't really a problem in my case.
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oh fyi I inverted the xrays and sharpened them some...