Caveat: The "border search exception" has some other pretty enormous holes.
As a non-citizen, I don't believe you need to answer any questions, but they may decide to just deny you entry at that point, and it could cause problems if you ever wish to return. Best idea I've heard of is to have your company encrypt the laptop before you travel and do not provide you the key until you're done travelling.
The one case I am aware of was when a CBP agent stated they saw child porn on the laptop, which the person subsequently locked. In that case a court ordered him to provide the key.
If I were concerned about traveling with certain data I would use a travel drive. Swap it in before going, and, as suggested, download what I needed once safely at my destination.
Now I'm wondering if there are other ways to carry that data with me in a format that would resist inspection. For example, on an SD card inside a camera. Or on a DVD. Break up the data into smaller files and named them variations on foo.jog or bar.avi or something, and reassemble things later.
For something like that the question might be whether I could be compelled to install or copy files to the active machine for inspection or evaluation if anyone got wise.
Planning to travel but got ITAR data on your disk? Better swap that disk unless you like fines and jail time.