I'd be careful adding that spacer. FSA cranks rely on having a specific distance between the bearings in order to get the proper preload (Shimano does not). you may find that after you tighten the cranks down that they no longer spin smoothly, or at all. I would advise simply avoiding that gear combo. It shouldn't be hard given that it's only the smallest cog. Shaving down that rivet will make upshifting to the big ring slower as that rivet is designed to pick up the chain.

One more thought, if you are currently using an 8 or 9 speed chain, switching to a narrower chain would yield a little more clearance to the big ring.