Adding Short Term Disability to Lawson

For 2011 our company is offering a new Short Term Disability (STD) benefit. The company will pay the premiums for 40% of an employees wages up to $750/week. The employee may also elect to purchase an additional 20% up to $1,250/week; for a combined maximum benefit of $2,000/week.

We have added the two benefits in Lawson with their respective 40% and 20% benefit of weekly pay; but the $750 cap on the company paid benefit complicates the calculation of the employee paid benefit. Once the company paid portion hits the maximum of $750 (at an annual salary of $97,500), then the employee paid portion can't just be calculated as 20% of the employee's weekly salary anymore. Instead it needs to be 60% of weekly salary - $750 (with a maximum of $1,250).

If you can give me some direction on how to tell Lawson to take a percentage of the salary and subtract out a fixed amount, please leave me a tip!

Thank you,
Trevor