Relationship problem

[koalas8717]

I have the next type of relationship in my DB.

LEFT OUTER JOIN epipe.estimatesubtypeconfig estc
           ON estc.estimatetype = d.estimatetype
              AND estc.estimatesubtype = d.estimatesubtype
              AND estc.config = tg.config

The problem is that the relationship involves 3 different tables (estc, d and tg), how can I create this relationship in Framework Manager? I know that you can create relationships between only 2 tables but my relationship needs 3 tables.

Regards!