Have you tried isolating the layers you want to work on, doing the trim, then restoring the previous layers? Layers can be very powerful when used correctly.
Win 7 Pro, 32 bit; Intel Core i5 @ 2.80GHz; 4GB RAM—Civil 3D 2008 & 2011
Credit where credit is due! Give kudos or accept as solution whenever you can.
I am very aware of layer isolate. I think it would just save a couple steps to not have to isolate and unisolate almost every time I want to trim something. I am always trying to find a way to save a little time designing.