Hi Leo,
It's impossible to combine members in row axis (like Entity A & B) - only page axis allows this. You have to create hierarchy parent for A and B in Entity dimension and then use it in report.
You can use same static approach for row axis.
B.R. Vadim
P.S. And for sure you can get data for A and B in separate lines, calculate sum using Excel formulas and hide original A & B lines....
P.P.S. And you can create a local members for each sum...