Problem solved :-)
Some old school VBA was required. Using the DataRecordSet object did the trick. It contains a method GetDataRowIDs that you can use to query the external dataset. Once you have the record to visualize, it's just a matter of dynamically updating the shapes with the correct record. Use macro recording to see how to do this.
MSDN: http://msdn.microsoft.com/en-us/library/office/ms195694(v=office.12).aspx