At the risk of being shot at, I’ll (cautiously) put my head above the parapet and suggest…
What if, instead of having the finish point at the airport (where the workload is the heaviest and the risk the greatest), perhaps have the finish point somewhere a few miles away. Put a series of countdown markers on successive paddocks that are easily visible from 500-1000’ AGL, and have the pilot make their finish call as they cross the last one. Observers on the ground can ascertain whether the aircraft is actually there when the call is made, and they can do so in complete safety. All the competitors will be coming from the same direction, so there’s little chance of crossing paths.
The downside that I can see is that it adds yet another call on CTAF (10 mile, finish, joining crosswind & turning base). You could use a chat frequency for the finish call, but that leaves the pilot fiddling with tuning when they should be preparing for the circuit. Dunno 🤷♀️