I converted one of mine by making a stop for the follower. Cut the flared end off a piece of 5/16 brake line, leave the mag assembled but slide the base plate forward 1/4 inch or so to open the back of the mag, load five rounds in the mag and slide the brake line up in along one of the corners until it hits the bottom of the follower, mark the brake line at the bottom of the mag body for a cut line. I used the JB Weld the NYS Police has insisted people use to glue the mag locks in the AR"s and put a dab in the lower corner to hold the brake line in place. The bake line will not hit the spring so you keep the full length spring with the proper tension and can still remove the spring and follower for cleaning. It's a bugger to get the follower out but it will come out, not really needed to clean it but you can remove it.
I found out the hard way, you'll want to cut that brake line a little shorter then the mark you make to allow the follower enough room to drop a little even with all five rounds loaded, make it so you can get five round in but not six. If you make it tight with five rounds then the follower can't drop a little when you insert the mag into the rifle with the bolt closed, the bottom of the bolt will push down on the top round a little. If you make it too tight you won't be able to seat the mag unless you open the bolt first.