Calculated member for epics the issues of some of which have a specific label


I’m trying to create a calculated member in the “issue” dimension, which shows all the issues of 4 different epics. But in 2 of the 4 Epics I only want to have the issues, which have a specific label.
Probably I should do this in “measures”, but I’d prefer to do that in the issue dimenion, using the aggregate function.
Anyways, I’m kind of stuck here. Anyone who could point me in the right direction?