Hi,
What you can try:
1. in the detail band, create a computed column with an "if" statement that has the value of the column that you want to sum if the group value is a "blank" and which holds a 0 value when it's not. Let's say you name it "cc_value_blank".
2. In the group summary you create another computed column which sums all the values of "cc_value_blank" for that group. Let's say you name it "cc_total_blank"
3. for the other totals you can then create a computed column that sums the values that you want to sum and add the "cc_total_blank" to it.
You might have to do a GroupCalc() or Sort() from code, since the different computed columns are referencing each other.
I think it should work, but am not a 100% sure.
regards