I always like the idea of having a table on a lonely beach.. with candles and food etc, and a surprise travel venture.
So, I suggest that you ask the Sheraton, or the Marriot (who both own boats) if they will set up a table for you on the Safliya island, and ferry you out there, and bring you back after two hours or so.
You can have the ice cube thing, (I don't suggest a dessert, as she may swallow the ring ! and then you'll have to look for it afterwards!)

If the hotels won't do the food thing, then there are lots of friends here on the forum !!! ... who you could bribe to be there on Safliya, and arrange the setting beforehand with a couple of guys who could act as 'waiters'.

Sheraton have a boat for hire for sure. There is also a guy called Basil, who does Paragliding... who could arrange something for you, by way of ferrying you out there, and perhaps helping to arrange the venue. Get his number from the Sheraton Recreation Centre.
Congratulations in advance.
Angel.