You would think that powder-coating the terminals would be bad,
ESD or no.
Maybe an answer would be using a conductive-material connector
"filler plug" which could at least short the pins (case-to-guts charge
would not be helped). Many sensors come with some sort of plug
to protect the pins from handling / shipping damage or corrosion in
storage. This would go away on installation so you don't have a
care about degrading your isolation spec. A clever mechanical
design might also include a tab that contacts the case "just enough"
to bleed charge, but not enough to bother the paint job?
Or maybe the customer / paint shop makes that all part of the
spray booth fixture "target mount" and solves their own problem.