I'm not sure a BM rep will know this one. Any gunsmith having both uppers could figure a way to do this.
I have, (in my hands now) a Carbon 15 flat-top upper. At the forward part above the gas tube hole is a set screw, allen head counter sunk into the aluminum picatinny rail. Looking under and up into the upper, I can see 3 clear circles under the rail in the carbon. This is either fill holes from where the upper was made, or more then likely where the aluminum rail is "set" in to the carbon. These set spotsstart right under the where the charging handle is, then the next is about 2.5 inches, down the next is 3 inches. The rail itself and the upper are mated with a taper, so it cant be mounted straight down and must be slipped onto the upper from either the front or rear.
I really dont want to take off my set screw, for fear of damaging the "zero" level of the upper. I may want to sell it sometime or use it on a light build.
Check your upper for waht I just described and see if it matches. I dont have camera, but if you do post some pics and I'll tell you if the mounting looks the same.