I just looked at the WW site and think I see what you mean now--are you asking how you can total up those selected items into just one single "Cohort" item? If so, try creating a calculated field like this:
Customer or Cohort
// If in the set, condense into "Cohort". Else customer name. IF [Top Customers by Profit] THEN "Cohort" ELSE [Customer Name] END
Then build your table like this:
Then turn off the header for IN/OUT.
Great. Glad to hear it!