Code To Copy A Row Of Different Formula Down

Trying to use a standard formula based on a variable workbook name. The INDIRECT solution suggested worked fine until I realised that I'd need to have the additional workbooks open in order to return the results.

Variable Workbook name in formula?

The reason I wanted to use a standard formula was so that I could use a piece of code I've written that would simply copy the formula from one cell and paste it accross and down for all cells within a range of rows and columns. Seeing as the formula now needs to be unique per column I need to change the code to copy the entire row of formula down instead of the one formula down and across. Here's my original code that copies a formula from B2 and pastes it down to the last row and across to the last column:

Code:
Sub CopyFormulaDown()

Dim lngLastrow As Long
Dim rngTargetStart As Range
Dim rngTargetEnd As Range

lngLastrow = Sheet3.Range("A65526").End(xlUp).Cells(1, 1).Row

[Code] .....

What I assume I need is to change the Range("B2") in the last line to Range("B2:???"), where ??? is the last column eg AA2. I'm not sure how to do this dynamically though.