FM Go could use some improvement in this area. Create a seperate layout for items such as taking pictures / signatures and use the default menu on these layout and your custom menu on all other layouts. You can still display the picture or signature on the main layout to give your app a professional look. There may be some better method to handle this, I just haven't found any. FM Go is still a work in progress compared to Filemaker Pro.
You can alway make feature requests at the following link