To the best of my knowledge, you can't use aggregate to sum anything not already in the data.
It sounds like you want something like:
shared numbervar fromSub; //which hopefully returns 0 for the other salesmen
SUM({table.field}, {group}) + fromSub
this would be legal, and cuts out the manual summaries / tons of formulas, but will only work at the salesman group level. You would need to modify the formula to update another variable so that higher groups have the same values. Like:
shared numbervar fromSub;
shared numbervar AllSub := AllSub + fromSub;
SUM({table.field}, {group}) + AllSub
HTH