Could the proxying capability of the old query.php also be provided in api.php?

At the Commons, we have a script that checks where on other WMF wikis an image is used:
http://commons.wikimedia.org/wiki/MediaWiki:Gadget-Check-usage.js

This script was written using query.php. Since it queries Wikis in other domains, it used the proxying feature of query.php (&proxysite= and &proxylang=). As far as I can see, the API does not have this feature, which means that this script cannot be rewritten to use the API. Using the current API, the script would need to make cross-domain calls (e.g., from commons.wikimedia.org to en.wikipedia.org to check whether an image was used there). AFAIK, browser security policies normally forbid cross-domain Javascript calls. Therefore, a proxy feature in the API is needed if this script is to rewritten. (It's currently inactive because of this problem, but while it worked, it was apparently used by many editors, who preferred it over the toolserver-based checkusage.)

Version: unspecified
Severity: enhancement