I would just like to point out that my second suggestion was just a piss take and that you should not try it! It was very irresponsible of me to even say it on a public forum where people who do not have experience with stock may read it and think that it is a good way to get them to move off the road.
As fweddy pointed out, you are likely to end up with an irate farmer (with just cause) to come flying up alongside you with spit coming out the corner of his mouth as he's hurling abuse at you and trying to run you off the road in order to share his views of that method with you.
But seriously, if you encounter one or a few sheep on a road/track that has banks or scrub on the sides they will just run down in front of you until they find a suitable place to pull off the road. The faster you go the fewer of those opportunities appear because they are thinking about getting away from you rather than looking for places to pull off the road. As David said, if you slow down or stop they will slow down and start looking for those opportunities and get out of the way quicker. Sheep don't like to run for the hell of it, they will almost always try their best to double back and/or stop and get out of your way.
If you encounter a mob of sheep being mustered down the road in the same direction as you then my first option above is probably going to be a better bet because if you slow down/stop then they will just carry on as a mob in front of you as if they are being mustered by the farmer. If you "go wide" in either direction (to put the most sheep on one side of you) then they will either stop or turn back and allow you to sneak around the outside. Again, this will all depend on how wide the road and verge is , how many sheep are in the mob, and how tightly packed they are.
If you encounter a mob of sheep coming towards you then you are best just to stop and wait for them to go around you. Otherwise you can edge forward at a slow crawl and they will just open up a hole around you as they flow past.
One thing you will notice when mustering (herding if you will) sheep is that there are:
- leaders, those that are always out the front trotting along looking for ways to go that the farmer would prefer that they didn't go
- followers, those that just plod along in the mob, usually trying to stay somewhere in the middle of the mob out of harms way
- slackers, the ones that always end up at the back and you have to push them along the whole time
- sickies, the ones that always fall behind panting/limping/collapsing and you sometimes have to carry on the back of the ute/bike because you can't wait for them any more
- cunning buggers, those that duck off into the scrub at any given opportunity and end up getting missed for shearing every year and end up like Shrek the ram (became world famous recently... somehow

)
So each situation will be different depending on the type and personality of the sheep.
Bloody hell... anyone would think I'm a sheep psychologist or something....

Sorry about the rambling!