You don't need templating ($1 etc.) for that as long as you can describe the holes somehow, which can be done out-of-band.

If we imagine a streaming protocol of key/value pairs that are either snapshots or deltas:

    event: snapshot
    data: {"topPost":[], "user": {"comments": []}}
    pending: topPosts,user.comments

    event: delta
    data: [17,{"comments":[{"body":"hello world"}]},"user"]
    pending: topPosts