Step 1: Head on over to My Plan > Income

Step 2: Open the Work section

Step 3: Press on "Add Job +"

Step 4: Select who is receiving this bonus

Step 5: Set a descriptive name in the Job field

Step 6: Enter the bonus amount in the Pre-Tax Income field

Step 7: Set the Start Age AND the Stop Age to be the month you expect to receive the bonus

Step 8: Set Growth Rates to 0.00%

Step 9: Press save