Maybe drain off half the 55gal water, save in a trash can or something for your next water change. Put your rock in buckets filled with water from the established tank, and dump all remaining water from the 29 into the 55. That should make conditions close enough for rock and softies.
If it were me, I'd just put the rock straight in without even worrying about it. I only baby the stuff that I think really needs it. haha