Often when I was trying to pass the reform, I pause the game on the following day, if it didn't pas. Then I would go through the log at the bottom of the screen and go through every single vote of the HRE members, noting them all on a piece of paper. Often the votes were something like 23-26, then I would know which members (often OPMs) that I should start to bribe. Often less than 5 is needed. A difference from -200 to 200 in relations can make a big difference in whether they vote yes or no to the reform.