Great question — answering as the UphillTech team:
Just ask for it nicely and politely. "Hi, thanks for the food, it's really yummy. If you have to happen some left over and it's not too much trouble, I would appreciate trying the pasta too." They may say yes, they may say no. There is quite a bit of variability in "friendliness" of the crew.
Full answer by Hilmar: https://travel.stackexchange.com/a/99763 (CC BY-SA 3.0).
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