You may be able to avoid all that by using a resin based temporary cement (olympian is one) along with a resin based temp material. When you check the fit before permanently cementing, note where the short margins are. Fill the cement in, and immediately contour where the short margin is, trying to fill the void with the resin cement, using an interproximal carver, plastic instrument or explorer. Avoid large overflow chunks in the immediate area because when you flake it off, the patch might come off right along with it. Clean the rest of the excess off as normal. The resin cement sets pretty hard for the short term and is pretty durable with the temporary. After two weeks when the patient comes back, the patch almost always comes off with the temporary as if it were one piece to begin with.
This way avoids the messiness and time consumption fiddling with flowable.