My Fitness Pal Premiere paid service allows for that ability now.
Can do the required 5 days to make eating goal whatever you want, and 2 days to make that what you want.
Sadly even that wouldn't integrate with Fitbit provided data well.
So you could at least keep the devices unsynced, and get a weekly TDEE value.
Then 2 days make it your 25% of TDEE, the other 5 days make it the average TDEE value.
Best Answer