The app called "Capacitive Buttons" can set the brightness of these but unfortunately, the app is supported only for Htc One series.
Capacitive Buttons app should work well on these devices:
- HTC One X (evita, North American variant, dual-core)
- HTC One X (endeavoru, International variant, quad-core)
- HTC One X+ (evitareul)
- HTC One
- HTC One S
Except these, there is an unofficial supported devices list which means that there's been at least one report of working app but no development effort has been focused on them yet.