CR won't call a stored proc except when the report is generated.
since the stored proc is not tied to a report, I would execute it from the stored proc that retrieves data for the report.
the other solution would be to return some trivial value from the stored proc and call it as a data source. You would need to link parameters to it (if they are needed). Though I don't know if CR will run a proc if it doesn't use the output...I've never done that...nor have I written anything to a database when a report is running, but that doesn't say it can't be done.