In Keynote 6 you can edit images on master slides to serve as Media Placeholders. I've created a theme for our company that has several slides with Media Placeholders configured like this.
Problem is that when someone adds an actual slide and clicks the media button on the placeholder a window pops up which apparently reads someones iPhoto library and only shows those images. Most of the images we use in our presentations are on the company NAS however so storing them in iPhoto isn't really practical.

How can I add folders to this media browser or make it so that when someone clicks the placeholder button, he can have a default Finder browser so he can select images from any location on his Mac?