I have been looking at all options myself. This is what I have found so far. You can in fact get permission for some short-term registered trips and tour operators. Ask your travel agent and that is not a joke, a good one has this sort of information, it is what they do. But although then legal, they are 'organised', however I was told I could purchase some latitude in that, maybe an extension in time and a personal itinerary! There is always a way and it is best to do it in this sort of manner rather than flout the law of a foreign country, because if nothing else it can become very problematic. At the extreme of incidents you could even be jailed, deported and lose future entry rights.

Otherwise you are forced to be illegal, relying on 'mates' and acquaintances to arrange something. Beyond anything else that has real issues with Insurance and so on, not just for you but anyone or anything you harm or injure.