If it's live rock you're talking about it's best to cure it before introducing it into your tank, then you can put in as much as you want all at one time. Here is an artile about curing live rock: http://www.aquariumadvice.com/showqu...aq=2&fldAuto=6
If you're talking about just normal rock you will be okay adding it, however IMO
waiting a couple weeks until the fish is eating and back to full strengh would be your best bet. If you do it now you will only stress him out more.
You should of course be very carefull when moving the rocks around, your best bet will probably remove him from the tank if you feel that you may harm him in the process.