Multiple States (weekly 60/40 split)

Kansas Resident, Missouri Employer, In-Office 3 days a week (MO), Teleworking from home 2 days a week (KS)

 

How do you handle an employer who does not have payroll software to handle 60/40 split between two states (does not recognize Form MO-4A Certificate of Nonresidence or Allocation of Withholding Tax)  and will be reporting incorrect wages per state on W-2?