When compensation is payable under this chapter for the injury or death of an employee employed and paid jointly by two or more employers at the time of the injury or death these employers shall contribute to the payment of the compensation in the proportion of their wage liabilities to the employee. If any such employer is excluded from the provisions of this chapter and is not liable for compensation, the liability of those employers who are liable for compensation is the proportion of the entire compensation which their wage liability bears to the employee’s entire wages. As between themselves such employers may arrange for a different distribution of payment of the compensation for which they are liable.