Filtering criteria using an Exit variable

Hi,

I have a requirement as follows:

There are 2 info objects for Start& End Periods of project.

There is another Keyfigure(number of months) which is populated by calculating the difference of Start & End periods.

Now, the filtering criteria would be Start period, End period and number of months.

When the user enters the Start and End periods of the project and also the number of months, the system shoudl display all the projects matching the above filtering criteria.

Eg:

Project1: Start period : 01.2009

End period : 06.2009

Number of months : 6

Project2: Start period : 02.2009

End period : 04.2009

Number of months : 3

Project3: Start period : 03.2009

End period : 05.2009

Number of months : 3

Project4: Start period : 05.2009

End period : 07.2009

Number of months : 3

Project5: Start period : 05.2009

End period : 09.2009

Number of months : 5

Now if the user enters the following the filtering criteria:

Start period: 01.2009

End period: 12.2009

Number of Months : 3,

the system should display only project2,project3,project4.

Any thoughts on how to achieve this using an Exit variable? Because the variables Start and End periods are created on 2 seperate info objects.

Thanks

Shyam