Ya know, since you already have an application, why not build a form/wizard to select the parameters for the report, and a) pass all the parameters (which allows you to validate them prior to the report ever seeing them) or b) get the dataset via your application and pass that to the report, then it doesn't even have to know about the parameters.
That is how my company's report work, the app gets the dataset and passes it to the report...the report never connects the database at all.
Just some thoughts, hope they help.