Steve, but it does for me exactly what you are describing.

WITH  MEMBER [DateOfSale].[LastDayOfMonthRevenue] AS 'AGGREGATE([DateOfSale].[Actual].[MonthSold].CurrentMember.LASTCHILD,MEASURES.[Amount Sold ])

This will show last child member which has value in the next level of hierarchy. And with AGGREGATE you can alter the Measure you want to show up.

Hope [@Alessandro Marin] can provide more info.