They might have a thermalight fuse sticking up from the top of the propellant. I staged Aerotech E6 motors using some old thermalight fuse material I got way back when FSI sold it. I read somewhere that was doable back in the late 80's and tried it with a modified Estes Apache 2. It worked, but even with a streamer I lost the upper stage to upper level winds carrying it away.