Option to Turn off 'Percentage of salary' amount when adding bonus amounts to employee profiles

We cannot currently add bonus amounts to the system as you cannot toggle off the 'Percentage of Salary' amount which shows up when you add a bonus amount to an employee's profile. Our bonuses are calculated using multiple factors so this percentage amount will confuse our employees as it is not correct. Please can it become an additional add on which can be toggled on/off?