Embedded report in workspace - no table join - pass search variable?

Summary

Pass a variable from one table into an embedded workspace report to present data from an un-joined table

Content

We have two custom objects that do NOT have a relationship:

• Add
• Data

Agents use the "Add" table, and view records in a workspace. 

"Data" also contains records, but this table is not joined to "Add". 

There is a field in both tables called "Pr_ID".

Is it possible to embedded a report on the "Add" workspace, that uses "Add.Pr_ID" to search for records on the "Data" table where "Data.Pr_ID" matches "Add.Pr_ID"??

I thought that using a variable (replacement value) would work i.e. variable "$id = Add.Pr_ID" and then set a filter "Data.Pr_ID = $id", but this then asks us to specify a table join.