Solved it myself!
A friend suggested that why don't I create the formula first of all
(using the drag selection method) and then convert the formulas to
arrays. Done a quick in Google Groups and I found the following code
(credit to Chip Pearson) which works an absoulte treat.

Sub ConvertFormulasToArrays()
Dim Rng As Range
On Error Resume Next
For Each Rng In Selection.SpecialCells(xlCellTypeFormulas)
Rng.FormulaArray = Rng.Formula
Next Rng
End Sub