Radio Shack make a product that does this, they are two small pyramids. Go to http://www.radioshack.com and enter product number "930-0757" to see them.

They are listed as out of stock on their web site, but you can probably still get them in the stores, if not, there's usually a few of them on ebay.

Here's a link to a bunch of extenders on ebay right now.

Rob