Hello, not a joke nor meant to be rude to anyone on a holy Sunday...but tried on my last hike in North Wales to urinate into a 1l-nalgene widemouth flask at night. it wasn´t overly cold, but I wanted to train for colder conditions. What I did is to open my sleeping bag half way, turned on my side and "attached" the bottle. The fuller the bottle got during the night (I had far too much tea for dinner), the more I had to lift my bowl during the process - a good exercise during Yoga, but a bit of a hassle at night.
I wonder if some of the male winter expedition cracks might be able to comment if that is the way to go or if there are better ways of doing it, like for instance to get up on your knees and pee like in front of a urinal but while kneeing.
As an intermediate result, it was indeed less hassle then crawling out of my tiny one-man-tent and getting into my shoes. At this stage I did not dare to put the full bottle as foot warmer into the sleeping bag, maybe some other time
Cheers
Chris