Hi JFriesen:
If you know the annual salary of the owner, you can determine their 'marginal tax rate'. Then we know that we want to reach
Gross Pay - (marginal tax rate * Gross Pay) = Take Home Pay - 500
Or, Gross Pay = (Take Home - 500) / (1 - Marginal Tax Rate)
Then you can go under Employees and update his annual salary accordingly to the new Gross Pay amount.
Note: this doesn't take into account any benefits, or vacation pay so if that's being included as well in the overall $500 you'd have to adjust for those amounts.
Hope this helps!
Lance.