Boats of opportunity are definetely the way ahead as far as training goes. Even if the skipper or captain is informed over the radio if you are just in the hover next to them, carrying out a recce and not going live on it. They are always more than happy to play along and very rarely decline. After all, it may be them you are called out to one day.
When asked if they are familiar with the hi-line transfer technique on the radio, and they are.... brilliant! Time to give them some more practice. If not, time to teach them, if you can get the winchman down on the deck via normal transfer.
Sometimes, if you refer the hi-line technique as a steadying line method, most will get the general idea.
In the RN, us guys get bogged down doing the same old Pas Boat day in, day out. Same s**t, different day, every day. Not so good as far as "playing the field" goes and getting a wide range of opportunity training. We are at Falmouth for goodness sake! Plenty to choose from, including one of the worlds busiest shipping lanes on our doorstep.