I would do something that puts the slider closer to the slot than two inches. Here's what I did, to a Banshee that was given to me already made with fixed leadouts -- it's got some contributions by other people, too. I'm not saying you should necessarily do this, just take it as an idea:
http://stunthanger.com/smf/index.php?topic=28339.0You could probably make a sub-rib, or just a pair of rails, to hold the leadout slider that will fit inside the covering of the tip. Then make the slot in the wingtip by duplicating the curved tip top & bottom. That should make for a nice discrete adjustable leadout guide.
Alternately, quite a few guys use ferrules stuck into holes in the wingtip. You drill a succession of holes in the tip, make a slot between them for the leadouts, and plug ferrules into that. Then you can not only adjust the leadouts but you can do so individually. It's a nice low-tech method that seems to make a lot of people happy -- hopefully someone will post a picture.