One of the things that is helpful is for those who want to be programmers to be in computer science in order to know 'programming'. That is, how if statements work, return, while loops, for loops, that kind of thing. It is easier for a person who is trained in teaching students to teach them how to program than it is for a mentor or another student to try. Even so, our team created a python training module that you can find
here. We went through this as a group and now most of our team is somewhat up to speed.
We don't actually pick people, instead they tell the captain they want to program, and that is that.