Are you saying you don't want to go to one table until there are only 6 players remaining? In other words, when there are 7 players, you should still be at 2 tables?
If this is the case, you can do a couple of things:
(1) Once you get down to 11 (or 10 or 9) players (however many such that you must be on 2 tables), you should start removing seats from the remaining tables, or marking seats unavailable. That will keep the players at two tables.
or
(2) Turn off Automatic player movement suggestions
or
(3) Ignore player movement suggestions
Then when you get down to 6 players, do as hemi said, go to the Tables tab and click the Suggestion Movement button.