To leave residual sugar behind you need to prevent the yeast from getting to it in one way or another. Pasturization can allow you to kill off the yeast in an already carbonated bottle, there are several members who do it on a regular basis.
You need to keep in mind that samples are your friend with that method. Samples that can be opened to guage sweetness and carbonation level. That can mean several bottles and I know you were only planning on making a small ammount. Just keep that in mind!
Also, please be VERY careful when heating a bottle with a Campagne level of carbonation...