Is it possible to "win" the port-a-diner pie?
I have had it work actually.. My first try so every attempt hereafter has been a disappointment.. It provided me with a 'Perfectly Preserved Pie' item that I crashed shortly after getting so do not know its stats. I do not know what affects the chance of getting it or not, I have pretty high Luck (9) so that may have helped.
If you don't want to take my word for it you can see a video of it being done here:
Yes, you can win it, although it seems to be as random as the programmed claw machines you play to win toys actually are. I won it after maybe clicking a machine twenty times - took it back to Diamond City and wanted to put it on my coffee table, but when I dropped it, it disappeared. So, be careful about not doing that. Stats on it are nothing special, but the feeling of winning it is stupidly good.