Thread a sporter barrel for suppressor?

Possible? Absolutely. It is a bushing, for those in industrial trades, but they are called "adapters". The barrel is threaded enough for an adapter to be screwed on to the barrel and the suppressor screws on to the adaptor.

Here are some examples http://www.gem-tech.com/store/pc/THREADED-ADAPTORS-c48.htm

Sporter barrels do better with lighter suppressors hanging off them. Also a 1/2-28 threading at the muzzle still needs enough shoulder for the mount to index squarely against. I believe both AAC and Thunderbeast publish tech specs with recommended minimums. This might help you decide where to cut and thread the muzzle. The Silencerco Harvester works well and a 1/2-28 mount is available and reduces tolerance stack and runout issues that adapters might introduce. cNC Warrior sells gauge rods that are cheap way to check end cap clearance to bore line. Really bad alignment is easy to see by bore sighting as well. Whoever is threading your barrel make sure they have experience threading for suppressors so they indicate off bore centerline and cut proper thread relief.