Damn. I don’t know how the S-Type keyboards are made, but if it’s even remotely similar to my old Vaio N505X, then it’s really annoying :(
I suppose the only possibility would be to send your notebook in to Sony for repair, or alternatively to order the right parts yourself. However, I don’t know if Sony actually sells single keys, keycaps or even the supporting clips themselves as single parts. You may have to order a whole keyboard.
Maybe groovy knows more?