Last time it happened to me I just cut off the pumps and began putting small pieces of filter floss in the overflow. each time you push a piece down the fish will swim closer and closer to the top. I had to almost fill the whole overflow up last time.
You do not even have to "fill" the overflow up with filter floss. If you just take a large enough piece and slide it down under the fish and then spread it out so it covers the whole overflow and then lift it up with one hand you can grab the fish with the other. At least that is how I had to occasionally fish out my mystery wrasse.......now I just have the overflows covered.