You can actually adjust the drill through text to a logically expression based on some other value including a parameter.
As an example, you may have a parameter that that has 5 different reports in the drop down....
Invoice Detail Report
Line Detail Report
Then when the report user clicks on a specific field... say a product id, based on the parameter selected, the specific report would open. Of course you could use the product id as one of the parameters for the report to be opened.
The drill through logic could either be a multi layered "IIF" or you could use "Switch" which I find a little easier to use and comprehend.