As far as I know, no you can't.
What you can do is to make the button transparrent and overlay it with a label.
Go to the format menu and bring the button to the front.
You can do anything you want with the label then.
Dave
I am interested in this link but cannot get it to work can you try re posting it please. I don't know if it just won't work for me or if it is the same for everyone.