This seems like a good idea, too bad it’s just a design concept:

Made of lightweight modelling clay and covered with a nylon and polyurethane blend fabric, Moldable Mouse can be kneaded into shapes by users.
[…]
Even the most advanced “ergonomically designed” mouse does not fit the preferences of every user. The inelasticity of the plastic model is problematic for long-time usage, as numerous people have suffered wrist injuries from extensive use in a fixed position. Moldable Mouse eliminates this problem with its unique design.
Moldable Mouse is made of non-toxic lightweight modelling clay, covered with nylon and polyurethane blend fabric. It can be kneaded into any shape the user prefers, and the shape is self-retaining. By allowing a wide variety of hand positions when holding the mouse, it reduces repeated motions of the same posture, thereby minimising the chance of common mouse-related injuries such as the Carpal Tunnel Syndrome.

(via)