There are a few options:
1. Try the coke bottle trick. Take the top, 1/3rd off and turn it around so the opening is pointing to the bottom and secure it. Make sure the hole is big enough to let him swim in. Add some frozen food, soaked in garlic. Hopefully he will swim in and get caught.
2. Leave the net in there for a few days, so he gets used to it. Feed the tank, near the net and try to catch him then.
3. Wait till lights out, find out where he sleeps and give him time to settle in. Turn on the lights and try to snag him that way. The element of surprise!!
4. Remove the LR
and catch him that way.
Now to prevent all of these, try feeding him and turning the lights out and adding the new fish.
Feed the tank, turn off the lights, move some of the LR
around and add the new fish.
Remove him from the tank and place him in a QT for a week or so. Let the new fish find a comfy place and then add the Angel back in the tank.
By the way, what other fish are you trying to add?