For a cursory search, disabling "Allow user switch" beforehand should work. For a thorough search, they will find the other profiles and require you to unlock them.
If we had a good backup/restore solution, the best way to pass a border check would be to make a backup, wipe the phone, copy some decoy data onto it (Candy Crush, some photos of cats/dogs, no social media), and restore the backup after leaving the border.
Unfortunately, we only have seedvault ;-) so restoring all apps is somewhat cumbersome.