easiest way to attach java moss is out of the water. this way you can do whatever you want to it without disturbing everything around it... then put the wood back. if you have to make the java stretch to get the look you're after then doing it in pieces will be fine. it will be easier imo to do it all in one clump if you can though. i'd just pull out the wood, place the java about where you want it, wrap it with sewing thread, tie it up and put it back.
