Try this:
Sub Totals_In_Blanks()
Dim lRow As Long, lCol As Long, lStart As Long, lStop
StartRow = 1 'Start at first row (Change to suit)
For lCol = 1 To 3 'Columns A to C (Change to suit)
lRow = StartRow
lStart = StartRow
lStop = Cells(65536, lCol).End(xlUp).Row + 2
Do Until lRow = lStop
If Cells(lRow, lCol) = "" Then
Cells(lRow, lCol).FormulaR1C1 = "=SUM(R[" & lStart - lRow & "]C" & lCol & ":R[-1]C" & lCol & ")"
lStart = lRow + 1
End If
lRow = lRow + 1
Loop
Next lCol
End Sub