Haven't seen any specific Imp to RS converters. I owuld recommend reviewing the Imp Catalog in detail, determine how close it is to the actual DB schema. You'll want to know how many computed fields were added to the catalog, as you'll need to replicate these for each/every query you run in RS, unless they are generic enough to add to views in the source DB.
*Theoretically*, if most of the queries are straightforward in Imp, you could take the SQL and simply put that in to a dataset in RS and then play with the display of the data on the report.