The problem here is the conduit is no longer earthed and could easily become live and is likely in some areas to be exposed. Plastic switches with nylon screws solve nothing.
How is it going to be exposed it is buried in the wall? If it's exposed anywhere else just Earth it, otherwise just do as Lee suggested. Life is too short to worry about this sort of thing.
Class 2 fittings won't solve the fact that the conduits aren't earthed. They need to be earthed whatever the type of fitting used.
Just do the job properly and don't try to dodge the regulations.
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