If you place FUD in water heated to 150F for 10-15 minutes, it will "relax" some and allow you to straighten the parts.
Then, all you need to do is hold them straight while they cool, probably at least for a couple hours.
Your models are printed "pefectly straight" in the printer, but because of the (heated) cleaning process, they can warp if they are excessively thin.
It's the same effect that happens in a thermometer
https://en.wikipedia.org/wiki/Bimetallic_strip
The other suggestions are good too: thicken the model, add some cross-bracing supports, or use 150F water to allow you to bend them back into place.
Oh, and.... yes, Shapeways, PLEASE find some other solution than the zip-lock bags for delicate models!
Years ago, I begged, pleaded and cajoled for models under a certain size to be wrapped in tissue paper. It worked, protected the models well, and the practice ended in less than a month.
I even offered to purchase at my expense and send in 10,000 sheets of tissue paper to help support the effort...
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