This thread on the Giant in the Playground forums presents a kobold mounted ranger build. The author uses the halfling outrider prestige class (from Complete Warrior) adapted for kobolds, stating that
it actually says in the halfling outrider description, under adaptation, that it can be used to exemplify any racial mounted class such as lizard riding elves, worg riding goblins, etc, etc.
The fourth post contains a breakdown of 15 levels of the build. The author mixes both the prestige classes wild plains outrider and kobold (that is, halfling) outrider and explicitly states that the latter is a halfling outrider adaptation and not a wild plains outrider adaptation.
But I can't find an adaptation section for halfling outrider in Complete Warrior.
Is there an official adaptation of the halfling outrider prestige class?