Retry-After header on 20X response -- HTTP/1.1 spec extension?

Dear Working Group Folks,

I am not a member of the working group.  But I have recently been tempted to
"stretch" the HTTP spec, and I'm writing to inquire if what I'm doing is
reasonable enough to eventually fold into the spec.

Basically I'm sending a Retry-After header on a 20x HTTP response.

I'm working with a "throttled" data service which rate limits connections.
Clients are harvesting a huge volumes of data over time.  Presently clients
get some data with a 200 result, ask again right away and get a 503
response, then wait out the proper Retry-After time.

If I can return Retry-After with the 20x result, it will cut the total
requests in half.  Clients can ask for data, and know immediately how long
to wait before they ask again.  Only a client that violates the timeout
would ever see a 503.

The HTTP/1.1 spec is pretty clear (in section 14.37) that Retry-After is for
503 and 3xx return codes only. Your thoughts?  Where would I go to suggest
an expansion of the Retry-After header, to be inclusive of 20x results?  Is
this a reasonable extension in your view?