I think that the issue you may be running into is that combat and social challenges are typically easy to design while incorporating several types of skills. Combat involves evasion checks, attack rolls, damage rolls, and several options you can take advantage of. During a social challenge, you will have to make checks for negotiation, con, intimidate, and a few others. But stealth? It often boils down to "make a sneaking test." There aren't a lot of other skills in the system that support it. There is palming and such, sure, but it's more niche. By large, the tricks that go into now being seen fall under the umbrella of a single skill. If you're running it with a single guy, design challenges that will involve more than just that, and make sure that you aren't just calling for multiple sneaking tests over and over again. Give him access to patrol routes and let the play work with tight windows, so stealth becomes just as much about setting up distractions and being in the right place at the right time as it is about having a high stealth modifier.