I like to use an insert, rather than a sleeve. It's a cleaner look when finished, and should hold up well that close to the tip. Essentially you're creating a spigot ferrule, but glueing both ends. I used a solid graphite rod that is sold at a model airplane shop. They have them in mm increments, so you can find something close and sand it to the right diameter. I repaired a 2wt this way and it still casts beautifully. There is a slight flat spot in the flex, of course, but it isn't something I notice while fishing. You'll have a flat spot with a sleeve as well.