Do they make inflatable handlebar covers/grips?
 

Something along the lines of a Serta mattress with it's "sleep number", so you could inflate your handlebars to your perfect "ride number" for cushiness or firmness?

I got to wondering after wrapping my new trekking bar in an old inner tube, and thought "that would be a great idea!" Since all my great ideas come in two flavors, "Already done by someone", and "stupidly unworkable", I was wondering if someone had done the "already done" part.

Not adjustable, but there's Cinelli bubble tape. I don't know anybody who uses it though.

somebody needs a recumbent..

To my knowledge, No. Time for you to build a prototype.

Some bar tape comes with gel pads to put under the tape, and you can fine-tune the firmness by how tight you wrap the tape.

Specialised Phat Wrap is one.