Feature request: Submit to a different URL as a background request, without sending the user there

[icopp]

I've got a few forms for big business sites where, rather than saving locally or POSTing to a different URL, things are set up so that it's a local POST with a confirmation page, which triggers a POST in the background (via AJAX or a server-side call) or a different URL. This is for use with secondary APIs (think marketing mailing lists, etc) that can ingest this form info but aren't really meant to look nice for users.