Can I enter a function as a selection in a pop up menu?

Hello,

I am trying to setup a budget numbers for my household. Some of our expenses are split down the middle, more is paid by certain individuals and some amounts change monthly. I have the monthly amount in column A, and in column B and C I have the amounts each roommate pays. Is there any way to manipulate the cell in column B and C and create a pop up menu so one of the selections is a function? So the function would reference a cell in column A that has the whole amount due. I would like something like =C7*.5676. So when I select that in the pop up menu it will do the math and populate the money owed by that individual in the same cell. Right now I enter a function in the drop down menu creator in format under cell, and the function does come up but only as text, it doesnt do the functions command.