This regulation is clearly made by people who don't understand the technology and capabilities of these devices. A waste of time and money; who is going to train customs officials to search through phones?
Why can't you just take a new phone and say, "it's empty because I got a new phone"?
Staying ahead of them with a technological trick is only a partial, temporary solution, though. Eventually you can expect that there will be an attack, whether purchased (see GreyKey) or legislated, on the workaround. What should happen is that the whole arms race should be nipped in the bud by outlawing this kind of data collection coercion. But I don't have a lot of hope about getting that genie back into the bottle.