I put some heat shrink on the spigot to extend it, then test fitted in my ear to make sure it wasn't too long.
I then rolled a slug of hot polymorph, wound it around the spigot, avoiding the hole on the end and seated the whole thing in my ear.
Once hardened, remove it and trim the excess heat shrink off.
I also tried proguard which is a 2 pack rubber for making earplugs. It moulded well, but didn't stick very well to the body of the Racal. You can wrap it around the body a bit to make it mechanically hold on.
Not sticking could be a plus if you think you want to remove it.
I think the foam plugs and proguard give a better noise seal, but the polymorph is cheaper to repeat so long as you pull it off before it fully hardens.