The simmer ring can easily be made from a piece of aluminum foil. Or, take a strip off a second can. The problem is, the holes are not as regular as on the Brasslite. So, you have to mark the stove and ring to make sure it goes on the same way. Simply mark the bottom of the strip for the location of the holes. Then, just nip off some "V" shaped notches opening each hole. Twisting the ring should cover the holes (mostly,) soo, they are fairly effective. But, between about 6:45 and 7:20 the change the burn time to 11:00-12:00 or not quite half. The reduction in heat is only about 1/3 and is actually too hot to do any real simmering with the Caldera Cone.
You would be better off following the design with a smaller center hole, and maybe 1/4-1/2" taller stove, compensating for the lower flame. A second stove at around 1/2oz is not that bad to carry and well worth it if you want to cook.