I almost always do the butt slide to start again, which means to straddle your CB and walk forward to get it moving, and then plop down on the seat where the pedals are already in a good position to immediately start pedaling, and while in an acceptable gear. On a hill it is going to be tricky since you will stop rolling soon, so it may help a little to take a little bit of the slope out of a hill by cutting across a lane or two at a diagonal when there is no traffic.
With all of that said, I simply don't stop on a hill that will be difficult to restart on unless I crash or cramp. When riding with friends I let them know that, and why I won't stop on a hill, before the ride even starts. So, I do a bit of route scouting to know in advance when the difficult bits are to make sure all my ducks are lined up before I even start it.