If you put Customers on rows, then right-click and choose Filter... Value filters... then you can choose to filter to only rows where Your Sales Measure > 100000. That particular approach won't perform very well until you upgrade to AS2012 SP1, but it
If you don't have your entire PivotTable filtered to 2009, but you want to filter based upon 2009 sales, then you could use my add-in to create a [Measures].[2009 Sales] measure and then use it in the Value Filters.
Probably the best approach is to use Excel 2010 to create a named set and specify the following MDX:
([Measures].[Sales],[Date].[Year].) > 100000
That MDX returns the customers with more than 100000 in sales in 2009. If you put that on rows, it will perform well and work well.
Do you think that covers your needs pretty well?