I recently had to solve this same problem with a change to some data used for
the charts. In my case, i had to chart This Year vs Last Year data, pulling
sub-totals out of a large block of cells

My VBA solution involved:
creating a string of addresses of the required cells,
copying the range,
pasting them into a contiguous range on a hidden sheet,
adding this range as a Named Range,
and assigning this named range to the Values property for the
seriescollection on the chart

You should be able to just step through and create your series string,
stepping by 5

As i cannot find my code, here is some pseudo-code from my notes:

Dim wkRange as worksheet
Dim wkOrig as worksheet

   Set wkRange = worksheets("InvisibleRangeSheet")
   Set wkOrig  = worksheets("originalSheet")

With Range

For i = 1 to cells(rows.count, "A").End(xlup).row Step 5
   strSeries = strSeries & ", " & .cells(i,1).address
Next i

   wkOrig.range(strSeries).copy
   .range(.cells(row,col).address).pastespecial
paste:=xlpastevaluesandnumberformats
   .names.add name:="RangeName" refersTo:=.range(.cells(row,col).address &
":" & .cells(row+wkOrig.range(strSeries).count -1,col).address)

   ActiveChart.seriescollection(1).values = "='" & .name & "'!" & "RangeName"

End With

HTH

sqlfan13