Well yes your approach sounds counter intuitive, particularly as there is nothing wrong with the 'strength' in your fingers. ..but your idea of fixing one finger (holding a key) whilst moving others is really the basis of Candia's work with splints (Sensory motor retuning). I worked with a splint for a while that fixed a finger in one position for a while whilst I exercised others. I made a little progress this way and Candia has had some success with the technique, but my improvement was nothing compared to that when reatraining under threshold and emptying my hand of tension.
