Options for Clipping References

Hi,

I have added a raised median in my roadway by way of linear templates for the curbs and a terrain+surface template for the grassed area in the middle.  I am able to clip out the portion of roadway along the curbs by setting clipping references.  However, I don't see a way to clip out the roadway in the grassed median portion between the curbs.  How could I accomplish this?

Thank you,

Michael