I had some experience of an electric one wheeled device called a 'Motor Mover' for moving large trolleys around a factory. It worked ok once it had the bulk of the weight of the trolley on it, otherwise it would slip.
A lot of the ones for caravans are designed to go on in place of the jockey wheel leg, which isn't much help on a tailwheel aircraft. A two wheeled one with something in which the tailwheel can sit would probably be the answer.
Something like this
mr shifta caravan mover | eBay
adapted into an electric version of this.
Or, off the shelf you can get this:
http://www.minimaxtugs.com/product_p/021taildragger.htm
