Use Kong Deck to sync upstream but not its targets

I’m interested in using Kong deck to maintain an upstream for each of my microservices. When a microservice instance stands up, it will register with the upstream. Once my microservices are running, I want to be able to use kong deck to update the upstream, but not delete the targets for the running microservices (since they aren’t in the yaml file). Is there a way to to this with kong deck?

The request-termination plugin is the workaround I am using:
message: I’m alive!
status_code: 200
plugin: request-termination