counting unique occurances of a charctrist over ANY selected period of time

I am on BW 3.5 and have a cube with date/salesrep/customer & a count (= to 1) per row. I need to know the count of UNIQUE customers sold to by the rep over ANY given date range.

I know, I know...there is a "How To..." paper out there that explains very nicely how to do this. UNFORTUANTELY, it is for BW version < 3.0!!!!! It has NEVER been updated for BW > = 3.0, and thus is NO HELP AT ALL!!!!!

Good luck with THIS issue, and thanks in advance for your help!!

Regards,

Mark Ulrich