If you are passing the string of report IDs to a parameter on the master report, I think using a table and subreport should work. You'll need a way to split out the report IDs using a dataset on the master report and return them one per row (so you can pass each report ID individually to the subreport via the details row of the table).
I was going to recommend a table-valued parameter for this, but since they don't exist in SQL Server 2005 check out Arrays and Lists in SQL Server 2005 by Erland Sommarskog for a few other options.