I have tried to slow my metabolism down with little success. You're talking up to 7000 cals/day - honestly! I have to take much of it in liquid form. I tried dieting more frequently (for several weeks actually), but this doesn't make a difference - your body simply gets back up to speed again...so by the time protein synthesis etc is ticking over for gains again after some weeks, your metabolism is "humming again". Not only that, but many people underestimate the amount that is burned from activity (not just resting metabolic rate), and that's high for some people.
There is one thing you can do though, and me and brother has had some success with it. Basically, you reduce workload slightly. If you train 6 days per week, reduce it to 4 days per week (workouts have to become very focussed/based more on compounds). If you do 3 sets/exercise, do 1 or 2 (as long as warmups are done, and keep warmups to lower reps).
This should "save you" up to ~1000 cals/week
Other than that, just add more liquid calories.
Most people who're heavily bulking usually hold their weight for some time (to solidify gains and/or to lose a little fat). They do this by eating slightly less than maintenance or at maintenance. It takes time but it works