Basically you need to cut the object in half, then make an instance copy of it. Then when you are done modeling you can tackle merging it back together.

First off you need an isoparm running down the center of the object (one that is in the center on the "front" side of your cylinder, and another on the "rear" side of your cylinder when looking at it from straight on). If you have these lines great, if not you need to make them by inserting isoparms.

Test it out on a simple cylinder. When you make the cylinder have it so that an isoparm runs down the middle, this will probably be determined by the number of isoparms are originally created. Then select these two isoparms, and detach the surface. Then delete the left side. Now make an instance copy of the right side. Now as you select and move CVs on the right, changes on the left should take place.

Good luck and let me know how it goes.