This isn't something that playmaker will do with the built in actions easily. While you can scale GUIs it's kind of a global thing. You can also do some limited things with textures. If you purchase a GUI editor extension with Playmaker functionality you will be light years ahead of any other option. If they're to expensive then maybe a custom GUI Skin on the asset store will do. Finally you can create your own GUI skins but not without some training and photo manipulation.
Don't forget that you can do some things easier by putting textures on a simple quad plane and giving it logic to act like a button.
Unity's new GUI system will be out soon, so you may want to wait before you start building something you might scrap later.
