OK here's my $.02:
Instead of staying with the shifter paradigm, why not go with something that is more suited to a CVT?

The sort of thing I am thinking of is a lever on the handlebars. This lever could be integrated with a brake lever in several innovative ways; eg pulling it normal style gives you brakes, while moving it up or down operates the gear mech.

For the gears, the lever would activate a engaging mechanism that enabled the CVT to change ratio continuously, up or down, until the lever is released. The ratio change would be operated by e.g. a worm gear; this would solve the problem of the CVT pulling hard on the mech when pedalling hard or when in a high ratio - a worm gear is a one way street, plus a very high mechanical advantage is possible to force the CVT change under any pedalling force. The worm gear would allow very slow and gradual ratio cganhges and be driven ultimately by the cog ie the pedal force. The drive gear would turn all the time, and the handlebar lever would engage the driven worm gear to change the ratio. Some way of changing direction is also needed, one direction for up, another for down.

All the details need to be worked out of course, this is just a concept.