Pimping/modding your Phantom seems to be popular. Here is the latest offering from our friends at goodluckbuy:
For a USD 329.67, you get a 5 inch display and a CF box to put the RC electronics in but make sure that you check the features before you buy: "For Professionals". (so you really are a professional :-)
The little thumbstick located on the left side looks handy for controlling a gimbal though.