Add headers for text match?

[mercul3s]

I'm trying to use Github's metadata matching to return code snippets/highlights in the response, as documented in https://developer.github.com/v3/search/#text-match-metadata. I know that I can add my own headers in HTTPoison, ie

header_list = Enum.to_list(headers)
    [{"Accept", "application/vnd.github.v3.text-match+json"} | header_list]

So I can get back something like this:

...
  "object_type": "FileContent",
  "property": "content",
  "fragment": "\",\n            \"key_limit\": 2,\n            \"owner\": {\n                \"email",
  "matches": [
    {
      "text": "key_limit",
      "indices": [
        16,
        25
      ]
	}
...

Is there a way to pass the header info during the client creation? I tried something like the following, but no luck:

Tentacat.Client.new(%{access_token: "#{token}", accept: "application/vnd.github.v3.text-match+json"}, "#{@uri}")

I also tried wrapping HTTPoison.base to pass the accept header, but I'm assuming that'll only work if I'm using all the HTTPoison base methods directly. Attempts to add text match as a header return results as a regular search api call. Any suggestions?