I've done this in the past but i've done it where the suitelet contained custom HTML that my client script loaded upon button click and used jquery to get any data I need with buttons in the suitelet. I'm not sure you can pass an object to the button click like you are expecting. Adding a button to the form should let you attach the client script but the client script can call the suitelet and get the response that the suitelet sends back (the data object you want)