Hi Gooliver,
Someone suggested putting rock rubble into a container and then putting the frags into the container. This seems to work for me for now.
I've tried fishing wires, rubber bands, squeezing between rocks, etc. Haven't had luck as these guys shrink and expand and darn slimy too.
The frags are doing nicely and polyps and colors are similar to yours so i'm assuming it's doing good. Hopefully, I will have one as big as yours is in a few years.