No, the nem will never be able to find the fish if they stay on the back wall.
If you have a large mesh bag or a fish net that can enclose the nem, put the fish food inside the net and place it over the nem with one end propped up so the fish can swim into the trap. When the enter to get the food adjust the net so they can't get out. Then wait and eventually they will get tired and host nem will sting them into submission. The relationship is more like a marriage than hosting.
Alternatively, if you get the fish inside the net, close their exit and then reach into the tank like you are going to grab them. The fish will dive for cover and the nem and the fish will live happy ever after.