Evan, it's pretty simple, so I hope not disapointing. Easy to make if you have a hacksaw, a drill, and a small file (a 3-corner file is best). The bracket from the stock tensioner is used. The lever is a piece of 3/4 x 1/8 steel bar stock. From your parts pile or hardware store you need a stiff spring, a 1 and 1/2 in 3/8 Grade 5 or better bolt, 2 nuts and a lock washer.
Drill a 3/8 hole at one end, another 3/8 hole about 2 and 1/2 inches from it, and at the other end, a small hole for the spring. The stock idler roller goes in the first 3/8 hole, but you need to use the file to shape the hole to accept the flat shaft of the idler roller axle. The lever goes on the 3/8 bolt. Put the bolt into the slot on the stock bracket where the idler roller axle was originally and run one nut on, the the lock washer, the the second nut; put on a little Loctite and use wrenches on the two nuts to make them TIGHT, holding the bolt in place such that there is a gap between the bolt head and lever so the lever will rotate on the bolt freely (this maximizes the clearance between the wheel spokes and the bolt head, as opposed to putting one of the nuts on the inside of the bracket). Put the idler roller into the filed-out hole, and connect the spring, and you are all done.
Being a bit compulsive, I used a buffing wheel and some Tripoli compound to really polish the idler roller axle bearing surface, and lubed it with wheel bearing grease before assembling, and put a little grease on the bolt where the lever rotates. Like the stock set-up, be sure the bracket is TIGHT on the bike strut and check once in awhile to make sure the whole assembly isn't being pulled toward the wheel spokes, as the torque will tend to do.
Not as professional looking as some of the commercial offerings, but as I had all the pieces on hand, my cash outlay was $0. Took me about 30 minutes and that included painting. The lessening of chain noise and smoothness going from coasting to acceleration was really was noticeable. Hope this is useful for you, and hope between the pic and my rambling I have explained it.