Does it help if the Japanese march everything straight across China? They could be at Tsinghai/Kansu J4 with air units nearby to kill off the Siberians on J5.
It would certainly help except I believe Japan has a big enough task holding off the 5 countries. I like taking China down to almost nothing before US gets involved, then take DEI’s, then try to withstand a full Pacific buy from the US. In the meantime, Germany should be able to make its way through Russia and its all up to the oil fields after that.