The following might work depending on the time you require for retail therapy in Lisbon:
Take the 09:52 Intercity train from Tunes via Setubal to Lisbon. This arrives Sete Rios at 12:59.
Descend, from memory I think, three levels to the Metro Station, known as Jardim Zoologico. Get a train in the direction of Amadora Este. Three stations down the line (i.e. a few minutes), and disembark at Estação Colégio Militar. Follow the signs for the Centro Comercial Colombo. You will then be in one of the largest Shopping Centres in the Iberian Peninsula.
There is a return inter-city departure from Sete Rios at 19:34 arriving Tunes at 22:45.
If all runs to to time it should give you at least 5 hours retail therapy.
