A report produced under the Web Console (formerly known as the private metric report server) has at least two datasets built into it. One summarizes job activities in a period, using the subclient ID as the identifier consistent between periods, job types and so forth.
Another dataset maps the subclient ID back to the client name, the agent type, the instance name or backup set name, and the subclient name.
The intent is for a user to be able to click on a subclient ID in a row ID in a pivot table of job data and have that link to data from the list of subclient data.
This looks like a match for what Books Online calls, "Creating a Preview for Data in Reports," but the format editor for adding a preview isn't offering me a way to say, "use this value as a look-up against that field in that dataset," like I'd expect.
Is what I'm trying to do what the "Preview" option under the "formatter" tool is meant for? Is my mental paradigm of this invalid? Is my explanation of what I want understandable? 
SP 17, if it matters.