I have a fish trap but its way too big for a biocube. Go on youtube and search fish traps for reef tank. Cut a small clear plastic bottle (water bottle works great) and invert the top into the bottom. Have some mysis or pellets in the bottle. Wrasse should go right in there. They get too confused to swim out.
Here's a link on someone catching a damsel
http://www.youtube.com/watch?v=Ym6MB...yer_detailpage
Best of luck!!!