crown molding and "S" hooks?

Hello I am new to all of this but I work for a company in Los Angeles. We are a design firm and we are doing a commercial space in NYC. Basically the client wants to hang pictures from crown molding using "S" hooks like at a gallery. We need to know what we might use and if anyone has molding companies that do this or know anythhing about how this works?

A good reference is like a.....
Picturell in old brownstone apartments, like a victorian detial, the idea is so that we do not put holes in the wall.

I hope this isn't confusing but anyone that knows anything about this please help.

Thank you