can an electric power shower be made safe if slides have been lost?

a buy to let flat has just been redecorated and new bathroom fitted. however the electric power shower has been re-used and replumbed. but the slides (or whatever they are called, the half thumb length bits of plastic that come out of the casing which the pipes go through the external casing) are missing. can the power shower be made safe by other means than these slides i.e glueing plastic over the top of these holes