Seconding all the folks recommending bending over! I'm one week from my ostomy reversal and sometimes plagued by really painful gas. I sit on the toilet, then bend at the waist and elevate my bum, and when I feel the gas shift to the end of the j-pouch, I quickly sit back down and push very gently. It's helping a lot. Good luck, we're in this together, man!
P.S. File all this under "things I never expected to write on the internet."