Trying to join two datasources in a listgrid

[anstaafl]

Smart GWT 2.5 LGPL, Jersey/MySQL back end.
I have a listgrid which (I assume) is already populated with values from the primary datasource.
Given the value of another field matching the value of a field in the field's optiondatasource resultset...

    ListGridField versionField = new ListGridField("version", "Version");
    versionField.setOptionDataSource(buildDS);
    versionField.setOptionTextMatchStyle(TextMatchStyle.EXACT);
    versionField.setFilterOperator(OperatorId.EQUALS_FIELD);
    Criteria c = new Criteria();
    c.addCriteria("sid", "sid");
    versionField.setOptionCriteria(c);

The sid field contains unique values common to both the grid and the datasource.
Also note that the sid field is not defined in the listgrid but is a member of both databases.
This is not working (big surprise there). ;-)

Can I do this at the macro level like this (somehow) or do I have to build something (like a formatter or editor) to deal with it at the row level.
I just need a nudge in the right direction.

Thanks