Thanks all, had a great day photographing 'living statues' with fill flash. Alrhough it felt a little bit confusing at times I'm pretty happy with some of the results Here's a sample:
Well I think in your original post you said you wanted a straight forward technique to give a natural light.
I couldn't tell you've used fill in flash in that picture !
Sporgon, thanks! Exactly the type of result I was looking for; flash without it being obvious. I even wrote your simple guidelines on a sticky note as a reminder. I ended up shooting most of my pictures in Tv because light conditions were varying too much (clouds, sunshine) to shoot fully manual. I did use the camera in fast flash sync as well. I'm really happy and think I've reached a milestone today (but still have much to learn).
5D3, 5D2, Sony α6000, G16 | EF: SY14/2.8, V20/3.5, 24/2.8, 35/2, Ʃ35/1.4, 50/1.8, Ʃ50/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200/2.8L IS II, 1.4x II, 2.0x III, 70-300L, T28-300 Di VC PZD | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC CS, Metabones SB | Vintage FD & FL glass.