Shower waste leak - question

The plumber finally finished installing the new shower this week, just in time for the kids to come home and Grandma to visit - hooray. It has been an unbelievably long haul. Unfortunately, Christmas evening we get a small swoosh of water dropping through the kitchen ceiling. So I think we can take it there is something he didn't actually test before moving on.

Fortunately (!!!) the overall job included a completely new ceiling/floor which has not yet been skimmed. I've whipped off the plasterboard underneath and can see that the waste is not fully sealed with the silicone they've used. It's just a drip, but of course that builds up and is no good at all.

Now my question is whether there is any advice about a reasonable short-term fix until the plumber comes back after Christmas (he has to do some other work on the heating in any case). I'm assuming the best permanent fix is to take the waste out and refit it afresh.

a) slather silicone on the underside
b) put a ring of silicone around the upper edge of the waste (which would have to be cleaned off the shower tray when the waste gets refitted).
c) gaffer tape
d) leave the plasterboard off and put a bowl underneath in the kitchen.