| There's 4 holes in the cam pulleys that the factory tool locates on. I'd try and use these rather than hold the pulley teeth. If you mark them you'll cut the belts up. You can use a peg spanner.
I used to use a 15mm ring spanner on the head nuts with a socket welded on the shank. Measure back from the ring to the socket, calculate the extra torque applied and adjust the torque wrench to suit. worked fine for me for years. | 
Threaded Mode