Used to call it "shooting" the guitar. (In days of old, were new instruments made of wood kept around the orchestra for the same reasons I wonder?). There's no perfect substitute for playing the thing, but shooting it will work. I've had instruments built for me which were so new when I got them that they'd not ever been played except for when the builder tuned them up. The changes (for the better) over the first several weeks are quite audible. One such guitar arrived with a very wonky timbre which I "shot" out over the period of a few days. Now, I chose acoustic music to do this, but I dare say anything that vibrates the thing will work. I'm just suspicious that wood needs wood as much as possible. Anyway, that wonky one is amazing now.

Carrying a guitar around in a vibrating rattle-trap old car helps too, so never go on tour in anything anyone would want to steal.

Peace, Mooh.