Ok so I partially hacked my way through doing this, by adding a column in WSS 3.0 to save the Encoded URL and using a workflow to populate that column.
Now I can add the EncodedURL field to the form, but my only option is to display it as a Hyperlink in the repeating table from the datasource. I don't want to show the full path, I just want the user to be able to click one of the fields in a row to open the .XML form that the data is from.