Stacked Column Chart Labels

Yeah, but you'd need to perform the calculations
on the worksheet and then change each data label
to reference those cells. For example, suppose
that cells A1:C3 contain
{"Category","Value1","Value2";"A",10,12;"B",20,15}
and they are charted as Stacked Columns. You could
enter =B2&CHAR(10)&TEXT(B2/SUM($B2:$C2),"0%") into
cell D2; fill right to E2; and then fill down to
populate D3:E3. Now click twice on the "10" data
label; type an equal sign (=); and click on cell D2.
Repeat this process for the remaining labels selecting
the worksheet cell with the corresponding calculation.

That's great - Thanks!
Just one more thing.
How do I edit the formula to include the currency symbol for the value?