Casting some solid silver ear studs - finishing the backs as part of the design...

[Madge]

Evening all!

I have been asked to make some earrings in the form of studs with solid parts front and back. I will (hopefully!) be making a model then casting in cuttlefish to create texture they have requested.
They have asked for a design similar to the picture attached where the back of the stud will also be the closure to the stud in replace of an ear scroll / nut that I would usually use.

Can anyone offer any advice/ experience as to how I can achieve the most secure closure. I'm trying to get my toddler induced sleep deprived brain to work out how to create a closure within the back?!

Thanks in advance!

Maria