You can try waymarking. The concepts comes from virtual caches, which currently are able to register only in a few geocaching portals, such as opencaching.de.
However, if your aim is to learn your friends to use GPS, I don't see any problem with geocaching. The most difficult part - finding a cache - requires some experience with geocaching, and it would be done probably mostly by you. But that part requires much more perceptivity and experience, than GPS skills.
What you can do is to learn them how to navigate to the direct neighborhood of the cache. Let's say, to the distance less than 10 meters from cache. Then, no matter if you find the cache or not, the leading person would be changed. The next leading person would have the task to navigate to the next cache. It means, he/she would need to analyse the map, find the optimal way, and then manage to get there using GPS.
The most difficult part can be to choose the good direction, if you want, you may bring a compass with you.