I use my cup holder, may not fit like a glove but it keeps them in place and almost vertical.
Wouldn't be hard to DIY one that fit like a glove if that's what your looking for. Start with a plastic cup, soda can with the top cut out, etc. whatever fits in a standard cup holder and your mod will fit down in. Position the mod the way you want it then pour something that will set up to sold around it to fill the rest of the area(you can go with any number of things here, caulk, liquid plastic, cement, etc...although dried cement might scratch the mod. Just be sure to put something around your pv first to protect it till whatever you use sets up.