I think you're asking for a way to ask the client to send data to a form without the client actually seeing that data. Unfortunately, the client has to see the data to send it somewhere, whether via GET or POST (or even PUT or DELETE), and you can't trust the client.

In short, no matter what you want the client to do or not do, the client can do anything it likes with the data you send it. If you don't want the client to do something with a piece of data, don't send it to the client.