Last week at AIA I had two different people ask me the same question - How do you get AutoCAD to trim to an object that is on a different elevation? Consequently I assumed there might be many of you who have run into the same scenario...
So here is your quick tip:
After selecting your cutting/boundary edges, select the Project option and switch the setting to View. This will tell AutoCAD to use the current view to determine the end result. You can also cut to the chase by setting the system variable PROJMODE to 2.