Forward meta-data to triggered build

Features Requests
1

Is there a way to forward metadata to a pipeline triggered via the trigger step?

- block: foo
  fields:
    - { text: foo, key: foo }

- wait

- trigger: bar
  build:
    meta_data:
      foo: # ? no way to pass $(buildkite-agent meta-data get foo)

I know this can be done using a dynamically generated pipeline, but it seems unfortunate to a require switching from yml to sh just for this.