One pressure point technique that I can vouch for working off the mat is what I call the "slimeball mustache (tm)". It can come in handy when you can't squeeze your arm under the chin enough to sink the rnc. It's fairly simple. Press your index finger over the persons upper lip, so that your middle knuckle is pressing into the divet (like your making a mustache over their upper lip with your finger).

I can vouch for that as well. We were taught to target that area (philtrum) for strikes and manipulations in American kenpo. Very painful and effective. "Where the head goes, the body must follow".
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin