Getting the US in in 1939 after Poland is attacked should be possible. Horrendously difficult, but possible.
Getting them in in 1940 when France falls might be easier, but still hard
Getting them in in 1941? Why? If they wanted to come in against the Nazis, they would have. If they're going to enter against the Japanese, you've got to have the latter attack the US first. I can't really see that.
If the Japanese attack Malaya and the DEI early, just hoping the US won't come in, it's going to take some months for tensions to build enough for war to happen. Note that Japan wasn't ready to invade southern Vietnam iOTL until the end of July '41, and they need to do that first, and take control of the area, before they can launch an attack south.
Basically, I don't see much realistic way the US can be brought in much earlier.
Maybe, just maybe, if the Uboots sink a couple of battleships in the Atlantic, say, that MIGHT work. But sinking the Reuben James iOTL didn't, so I'm not sure what it would take.