I have no special knowledge on the subject, but I did a quick Google search. I'm sure you might have run across some of these before, but I wanted to share them since I'm pleasantly surprised by the depth of things that are out there.
* http://www.gamespot.com/articles/modder-creates-single-hande...
* http://www.oneswitch.org.uk/1/AGS/AGS-bespoke.htm
* http://kotaku.com/he-built-a-custom-controller-to-help-disab...
* http://www.game-accessibility.com/index.php?pagefile=motoric