Operation on ranges

Is there a way in which I can perform on an operation on a range within a function ?

For example, I have two columns - column A and column B. I am interested in computing the sumproduct(col A, col B) which is a straight forward function call.

Now, instead of computing sumproduct(col A, col B), I am interested in computing sumproduct (col A - fixed value, col B) ie I want to subract a fixed value from each element of one of the columns. I say fixed value, but the value is essentially another cell in the table which is dynamically generated.

On straightforward solution is to create another column which represents col A - fixed value. Is there a way to do this without having to create a new column ?

If I've missed something obvious in searching for a solution to this, please can you just point me in the right direction ?

cheers,

Vikram