We had the same issue.

We have a dynamically assigned security model that allows different levels of heirarchy in an organization to view data by creating where clauses which include or don't include data contained in our dashboard pivot grids / graphs. Basically with any field that we supply in our dashboard queries, we allow the end users to limit data that is then viewable by subordinates in an organization (a CFO can limit a regional manager's access to the exact same financial query by say division, the regional manager can then limit a branch manager's access by branch etc...). As the where clause is generated further down the list getting more and more specific, often times our where clause has exceeded 8000 characters. Our solution was pretty simple, we'd use a temp table with one text field, build our where clause into that field and then at the end of the where clause generator, simply perform a select on the text field of the temporary table... this is then added to the query inside c# code that generates the dataset.