The Constitution allows the States to apportion thier EV in any manner they see fit. The state legislatures are voting to merely give all their EV to the candidate with the highest popular vote. So its doable...
They have wide latitude, but they cannot do “as they see fit” It must be representative of the people, in other words republican. Having the state legislature vote vote among themselves, appointing a committee of citizens from that state, a popular vote of the citizenry, etc. These place the vote within the state, as it must be. Allowing other states to decide does not represent the will of that state’s voters.