You can simply block them from doing so the old fashioned way, with screens (SZ 37, SZ 43, SZ 44). They can move past you at any time, except when they declare war–then they can destroy your blocks during Combat but they can’t combat past them to Amphib. Only downside to all that is you only get 5 (6, if you count the very movement restricted US DD) ships to accomplish this that you’d probably rather save.
If Japan intended to stay at peace, then it passes right through you as a bizarre “Armed Imperial Neutral” (ie Japan can hang out in SZ 26 or SZ 39 at peace) so then you can’t block them anyways.