Bank roll management does not work with such a small roll. Don't bother building it up before playing.
Option #1 - You play 100 hours (or whatever) of
freerolls, get an OK bankroll and play with it. You may lose $7 right off the bat, but your bankroll allows you to continue, or you win and continue.
Option #2 - You play with the $7 and lose it. You continue to play freerolls and taking the money to tables until you quit running cold and build it up.
Option #3 - You play with the $7, win with it, and never look back.
In Option #1 you are guaranteeing yourself a lot of extra time at freerolls. Immediatly taking the winnings to the money games guarantees the least amount of time possible in the freerolls. And believe me, it's a lot easier to make money in low stakes money games than in freerolls.