What I'm doing is cleaning my cc weekly, very well. Moving the rock around and cleaning under them. I'm also taking some cc out when I do my waterchange, a few net fulls. My levels haven't changed, since the cc is cleaned before I move it out, thus nothing is released into my water. When I have all of the cc gone, I'll put in the sand.
So, clean the heck out of the cc, (I forcus on 1/3 of my 75gl at a time) then remove part of what you just cleaned. You'll need to move your lr around, it's yucky under rocks that haven't been moved in awhile.
I've found using a net to remove the cleaned cc doesn't make that much of mess and doesn't cloud the water.
Though, remember to watch for inverts when moving rocks....you don't want to smash something. I have two stars that are hanging out in the big pile of rocks in the middle of my tank...