autozen is absolutely correct. You can lose bunches of fluid from the supply hose and the clutch master cylinder itself with no problem as long as you keep the reservoir full. This is because from the bottom of the clutch m/c up is a straight uphill shot and the bubbles can work their way up. It's between the master and slave where you have bleeding trouble.

Bleeding bottom up is definitely the ideal method, but I've had good success over the years just bleeding it two man method and then letting the bubbles work up into the reservoir.

Good luck,