There is a difference between a pax briefing and a crew briefing.
I think what you would want to do on a commercial ride is a crew briefing. This basically consists of initital heading, altitude and speed from your clearance, emergency procedures for dealing with an abort, loss of an engine, or fire, and any other information that may be pertinent to the flight. Be sure to delegate responsibility for tasks in the event of an emergency as the DE is a crewmember. For example in the event of a real emergency you need to designate who would fly the airplane and who would deal with the emergency and you need to give this info in your briefing. I think if you cover the basic stuff including the emergencies the briefing will satisfy the PTS requirements
As far as pax briefing it is mostly a safety briefing. Locations of emer exits, seatbelt use, oxygen use, location and use of lifevests and/or rafts, etc. If you are taking your checkride in a 172 all this is kind of meaningless as the emergency exits are obvious (doors) no oxygen, no raft usually, and the seatbelt stuff should be on your before takeoff checklist.
In addition to the crew brief that flydog mentioned, I think it would be a good idea to give a pax brief to the examiner as well. I always reviewed this with my students at least once towards the end of their certification process b/c that is when they would be taking their family and friends for rides. You should cover the use of safety belts, location of fire extinguisher, location of all exits and how to operate them, use of oxygen, location and use of flotation devices and raft, assist in looking for traffic, explain the sterile cockpit idea, tell them to keep their hands and feet off of the yoke and rudder peddals unless you tell them to, explain that they may hear the stall horn during landing and that this is normal, and to let you know if they are feeling ill. You can skip the ones that don't apply to your flight (ie oxygen, flotation device, or raft). Yes it's alot, but the examiner will tell you that they get the point and to skip the rest and to continue with the flight.
This is not mine, nor do I take any credit for it, The author is a girl at my school.
"There is no smoking, eating, or drinking on this flight...we don't need a vomit-comet. There is one exit in this aircraft, its the one you came in through. It's a door, it opens out, the handles are self-explanitory. Your seat is equipped with a seatbelt. Seatbelts must be worn during taxi, takeoff, and landing. To fasten your seatbelt, wait a minute.....if you don't know how to fasten a seatbelt, maybe you shouldn't be out alone without your helmet on."
SW Pilots: I think you should add this to your list of amusing briefings, lol
Assuming you're not going out for the first time, doing aerobatics, or going over water, my last boss hollered out WITH ONE BREATH the following as he fired up, pulled his seatbelt on and taxiied out:
"Hey, my name is Tom, just like it says on the tail. Keep those seatbelts on at all times, there'll be no smoking, drinking, or shooting at the pilot. The ELT is located together with the survial gear in the rear of the aircraft and operates automatically, the fire bottle is under my chair, and if you get curious there are briefing cards in the seat pocket in front of you. We've got three exits, two at the front and one at the rear, just pull on the handle and push out on the door. If you need anything, my name's still Tom and have a nice ride!!