Not possible, the sensor and processor are tightly integrated. If you upgraded the sensor, you'd need a faster processor and upgraded firmware to make it all work. Basically you need to replace the entire camera.
The new cameras coming out soon are going to be the best available upgrade path, though at present the new large sensor camera (E90) is not compatible with the Typhoon H and is only available for the commercial H520. There are rumours that a firmware upgrade will fix this later on though, so we're waiting for further news.