Parameter options and expression language

We have a REST service that orchestrates our deployments that spinnaker interacts with.

I’m looking to have an approval stage that operates on state exposed by our service (the list of blue services that are ready for promotion) (regulated environment so needs human in the loop)

It exposes a REST endpoint with information, is there any way of mapping this information to parameter options for selection by a user. I can use the spel to hit it fine, but can’t see if we could map this to options?

I guess generically in a capability i’m looking for a way of taking parameters from a REST endpoint that a user can select from during invocation or manual gate when invoking a pipeline.

If this isn’t possible looking for advice on options to achieve this, webhook trigger maybe?