Heres what I did yesterday to make a lid for a standard keg with an oaking ss wire insert.
I removed the central part of the spear which left the outside screw in housing. Then cut off a chunk off oak with a hole saw, sanded back to just fit inside and bashed it in with a hammer.
The ss wire I used is actually marketed as a kebab skewer. Its got a premade loop at one end and a blunt needle the other end for passing through the meat and veg. I was going to get a bit of ss cable from bunnings but found this at the back of my bbq and thought it'll do nicely!
The ss wire I passed through the centre hole of the oak bung and threaded on a mix of toasted and charred american and french oak sticks. I quick knot in the end, feed in the "chain" and the lid just screws back on the keg.