I was able to do this using an extra expression. It is not as pretty as if it is in the same column.
Another way you can do it (Also not pretty) is to create another dimension, something like if(Accountcode1=1 or Accountcode1=2,'Account Code 1 and 2') Then Check Show Partial Sums for Account Code 1 dimension.
I don't see how your workarounds work marcsliving; especially for partial summing account code 1 : i need the custom line to be really intermediate; original dimensions organisation should be in place before and after it.
The source of my problem is that drafts were made from Excel, and Excel is much more flexible than QV (not the same purpose anyway).