It's unlikely to be that simple. Consider what might happen if the US detects what it believes are invasion convoys approaching the Phillippines. In reality, these convoys aren't going to the Phillippines, they're going to the DEI - but the reports don't say this. At this point it's fairly easy, IMO, to authorise a "pre-emptive" attack on the convoys using US aircraft on the Phillippine, and particularly easy if you're following policies of hostility to the Axis powers. Japan will, of course, retaliate, and the whole problem of a declaration of war goes away in a self-fulfilling prophecy.
After the war, of course, evidence might come to light that the whole thing was a colossal mistake, or even a deliberate US conspiracy to enter the war - although the absurdity of attempting to seize the DEI while leaving a hostile base across your lines of communication argue against this. But that doesn't help Japan.
Consider Japans Naval losses from Dec 1941 to April 1942
5 modern Destroyers, 3 old Destroyers, a Frigate, 6 Minesweepers and 8 Submarines, are you seriously suggesting the American forces in the philliphines, which were substantially weaker and less well prepared than 18 months later were going to do anything other adopt a confused posture. I think it's a scenario where dithering and uncertainty are bound to ricochet back and forth between the various levels of Naval Command, the Whitehouse and their diplomatic services.
Just exactly what aircraft on the Philiphines are going to be available to
sink large numbers of Japanese ships and turn back an invasion of the DEI,
if they couldn't do it in early 1942 they were not going to do it in 1940.
And it's not uncommon to have hostile bases across your lines of communication, it's part of bypassing enemy strong points.
As was said earlier the US is unlikely to declare war.
If the Japanese do occupy The DEI in the summer of 1940 then i think they are better placed to prosecute a later war. They can commit more forces to the Indian ocean to deal with the British. It does surprise me that they
failed to take advantage of the fall of France to eject the British from
the far east before turning on the Americans.