Actually, jsut having gone through the (painful) process and speaking to 2 doctors and a sports physiotherapist, it is best to leave the shoulder dislocated and let a doctor do it. Reducing it yourself/with first aider should only be done in an absolute emergency as you can really do alot of damage if you dont do it properly.
But you are right- it is a good skill to have especially if you are on a multi-day trip. Fortunately, we were able to get me off river within about 2 hours of it happening.
Now that I have a few weeks to "reflect on things" I will probably sign up for a wilderness first aid course myself..