ActionScript 3.0 :: Cache / Copy Bitmaps Loaded From External Source?

I'm working on a chat application that retreives user profile icons from remote sources (e.g. Blogger, Yahoo, Gravatar, etc). Easy to get the images in a Loader and display them. The problem is that a single thread could have hundreds of records, but probably only 10-20 active commenters. In a standard browser, each <img...> link after the first one is cached, so you only hit the source site once. Is there any way to cache/store/copy those images within Flash to avoid requesting the same image over and over?

I can do it in the Local sandbox by accessing the BitmapData of the loader content and cloning a new bitmap for subsequent instances of the same request URL, but of course once the application moves to the Internet the security system requires a Policy file allowing bitmap access. I don't need to manipulate the bitmap at all, just copy it. Or reference it as content from multiple Sprites, or something along that line. Once I've downloaded the image once, I don't see why the security system would prevent me from displaying it unchanged as many times on the page as needed.