I have made a couple of useful macros that used to be assigned to individually designed buttons in Office 2000. In Office 2007 I can choose only between a number of custom buttons for my macros. I know I can use several ribbon editing tools to create my own ribbon groups and buttons, but I would rather just add some images to the location where Excel 2007 stores its custom buttons, so that they show up among the built-in buttons from which I can choose. Does anyone know where this location is, and if it is possible to add my own images/buttons?

Regards, Martin