Did you ever look into replacing your foam with DSF? I also would consider a grounding cable running from the motherboard to the GPU to the PSU case. I had to do that with some Paladins for some really super ESD prone environments.
I'm currently not running any foam at all in the system. I looked into a non-conductive spray coating (used in the other Pelican Case VR build) but it was $60-70 a can. I looked into non-conductive foam but apparently there is a lot of foam that is just dyed pink and passed off as non-conductive, as opposed to actually being legit. I can probably scrounge some from work but I don't know how well that would help remove static build up vs protect against passive static during shipping.
How would you go about grounding the GPU?