Yes beagling works but from my experience at some point during a lengthy casting session one of the pieces of aluminum tape will fall off unnoticed. I have used 4 different types on tape (high temp and regular) and have not found one that won't eventually turn loose without warning. Just saying...
I have considered taking a spring load center punch to one side of the mold but keep chickening out. But I do keep thinking the spring loaded punch would be more likely to displace the same amount of metal with each punch.