OAB -- Waiting period

We are going to change the waiting period (for benefits coverage), so that Dependents coverage starts after 90 days from hire date (Employee coverage is effective after 30 days from hire date). How do I setup plans so that employee is charged “Employee Only” rate unti dependent’s coverage kicks in after which different rate (“Employee & Spouse” or “Employee & Children”) is applied?

For example:

--Employee hired on 01-JAN-2012

--Enrolled in "Employee & Spouse" Option

--Employee Eligible for benefits from 01-FEB-2012  (Coverage and rate start date is this date)

--Spouse's coverage starts on 01-APR-2012

Now we want to apply "Employee only" rate between "01-FEB-2012"  - "31-MAR-2012"