If an officer flashes a badge at me and told me that it's ok for me to leave my vehicle when I asked to go take a piss while pulled over, I think it's pretty much common sense not to leave my vehicle to be planted evidence.

In Lance's case, his vehicle is his body.. he should know better to stay within sight of the inspector until the credentials are varified and samples are given to satisfaction. Whether to provide samples before or after the varification could be decided by Lance, but stay within sight of the inspector is probably the safest approch to avoid confusion.