You can do this by creating a new pay code under the Setup > Pay Codes screen. The pay code should have the Payments tax type and be called something like Second Bank Account (note the account details are left blank on this pay code):
Add this pay code to the employees default pay codes under Setup > Employees > Edit employee > Default Pay and edit the pay code to enter the details of the bank account, particulars, code and reference and the amount to be paid into this account. Fixed payment amounts can be made to secondary bank accounts by entering the amount in the Default Rate field.
The remaining pay amount will be paid to the DC pay code, or whichever other system payment pay code has a zero default rate.