In an API Blueprint document, can I combine a model with headers?

The “model” facility seems intended to reduce duplication — when specifying the requests and responses to various methods on a resource, the same body will frequently be specified multiple times. So one can define a “model” and then “refer” to it within various request and response “payload” sections.

So I’ve defined a model like so:

### An Event

* Model (application/vnd.document+json)

            {
                "_type": "document",
                ...
            }     

and I can then refer to it in various places:

* Response 200

    [An Event][]

which works great; the output includes the entire model body in place of the cross-reference.

However, I can’t figure out how to combine this reference with a request or response header.

I’ve tried various formats along these lines:

* Request

    * Headers

            If-Match: some-etag-value

    * Body

            [An Event][]

or

* Request

    * Headers

            If-Match: some-etag-value

    [An Event][]

with no luck.

Is there any way to do this?