I clear some free time--as much as possible--the day of my session. I like to think of it as my 'designated' rumination time. I ruminate. I regret. I journal and do something quiet and solitary. Then the rumination time is over and I do other things. I compartmentalize.

I found my rumination got a lot better as soon as I allowed myself to do it instead of feeling weak or guilty or indulgent for thinking about it. Would something like that work for you?