Hate to ressurrect a dead post... but I figured I would try to contribute....
http://www.plastruct.com/Pages/Properties.html
http://www.plastictroubleshooter.com...melt_temps.htm
I don't know if you use plastruct, but the info they have on their Styrene may be helpful. They say they use "Hi-Impact Polystyrene" and at the second link it says Polystyrene has a melting temperature of 350-390 degrees F. 150 degrees C is about 302 degrees F. That's quite a difference, but I don't know the temperature at which the styrene softens... and I think that's the information you need most.
The best idea I can think of is make some sort of dummy part to be molded and see what happens from there.