Actually, yes, you can.
However, you can't do it from MyDisneyExperience.
To make this work, don't link a credit card to your MDX account in advance. Instead, go to the front desk of the resort at check-in and explain that you want to link more than one CC to your account, and split the charges a particular way. They do it all the time, and most CMs know how to do it instantly. If they say that it can't be done, give them a friendly smile and ask them to call their supervisor over, because all of the supervisors know how to do it.
These two MagicBands charge to THIS card... those two MagicBands charge to THAT card... all done. They can even add a separate card for each MB on the room, if you wanted to go that far.