Accurate analogue low pressure controls are hard to come by for gaming. Presently, it is possible to remove and/or replace springs in some standard thumb-sticks. It's possible to use Makey Makey and the like for ultra-light digital switches and use JoyToKey to adjust the pressure incrementally. The Razer ONZA Xbox 360 joypad is perhaps the smoothest and lightest pressure off the shelf standard joypad controller. Sometimes, though these are just not light and accurate enough.
This is where the fascinating controller and game accessibility work of Graham Law at Celtic Magic looks like helping out. The videos above show some ultra light joystick and controller reduction methods. As this system is seen as a standard joystick, it should work with JoyToKey and the likes of the Titan One to open up a huge array of ways to make gaming more accessible. Exciting stuff to open up 2015 with.