They should just get a CIA or FBI profiler to come in and "read" their mannerisms to see which actor is lying. Or give them lie detector tests. I don't think the average actor is good enough to beat the lie detector.
One thing I have to agree about...a good actor could react to reading lines with a Rottweiler on the other side. There was no need to wait for Ellen Pompeo to read the words. The average production assistant can do a fine job of subbing in for an actor in that respect.