I switched to a sling pack about two years ago, and haven't used a net since that time. It bothered me at first and I looked for a solution. One solution that was recommended to me was a "NetHolster" made by Smith Creek: http://www.smithcreek.co/net-holster.php
After a few months, though, I became accustomed to fishing without a net, and thus, never purchased the NetHolster. Very few fish require a net, and I guess I'm at the point where I am often thankful when the fish gets off the line just before reaching my hand - no need to handle the fish or take the hook out.