But really, people should just superbump good topics whenever they think to do so, and not worry about this sort of strategizing.
I'm not concerned that much about my own bumps, just looking for loopholes that farmers could exploit. It looks like if they have ~30 high-merit accounts they could keep one or two threads super-bumped to the front page. Likewise if they have a bunch of high-merit accounts they could also mini-bump multiple threads. That might be more feasible since mini bumps don't cost anything (other than maintaining earned merits) but they would need a lot of accounts to overcome the 7-day limit.
Those sound like very costly scenarios so likely not a big deal.