Excel 2013 :: Unique Count In Group SubTotal

Using Excel 2013.

Is it possible to get a unique count in a group subtotal though the elements in the group may not be unique using Pivot Tables w/o resorting to Power Pivot?

Ex

Group 123
Group 456

Are both members of NorthDivision

If someone is in Group 123 for 9 months, then Group 456 for 3 months, that membership should be reflected in the correct group accordingly.However, that person should only be counted once in the NorthDivision, not twice.

Output:

Group 123 0.75
Group 456 0.25
NorthDivision 1

At first glance, it appears easy, however, what if membership is only total 3 months?Then Group would increment 0.25, but I need NorthDivision to increment 1