Did the watch repairer try a screw remover (see my post above)? They come in different sizes and I imagine they make 'em for watch sized stuff too as they really are the only "non-destructive" way forward (unless you are lucky with one of CreamyG's suggestions). I used one for a very small screw on a laptop.

I note in Nokia's service manual they emphasise not to reuse screws after disassembly - I guess they know they are "soft".