Forcing last level of location while creating the requisition

Content

1. We have four level of Location.

Country, State, City, Work Location

2. Customer using People soft as HCM Solution and there is requriement to flow information from Taleo to Peoplesoft.

     In Peoplesoft there is concept of Location COde.

3. We are matching Location Code with Work Location (4th level) at Taleo Level.

It means that we have force 4th level of Location in Taleo otherwise we can find location code in peoplesoft.

Problem:

========

We need to force the user to select the last level of location while creating the requisition.

How we can do this.

If this is not what is other workaround for same?