Again... I'm no expert having only done one MC. I believe you will not be getting the maximum benefit by going off the Master-Cleanse for two days on the weekend. However, I feel EXACTLY the same as you in that I can do the Master-Cleanse all week easily. On weekends I'd rather eat healthy for those 2 days and go back on the Master-Cleanse again each Monday. I'm sure it's not ideal. MC purists may not like the idea... but I've made such great progress on the MC I would really like to continue for an extended period.
I started with one 11 day cleanse... and I'm starting another 14-21 day cleanse on Monday. After that I plan to eat healthy on the weekends and do the MC during the work week. I can't see how it could possibly hurt... plus it's pretty amazing how fast you can lose inches off your waistline on the MC.