A Bing search shows that there is a project on CodePlex called CrissCross that might do what you're after.
It can be found at: http://crisscross.codeplex.com/
The description on the site says:
CrissCross is an open-source ASP.NET application that provides an alternative front-end for running SSRS Reports.
That is, a way of running SSRS reports that is like the 'Report Manager' that comes with SSRS, but different
and more customisable. It is built using the standard ASP.NET ReportViewer component and the SSRS web
HTH,
Rob