How do I handle computed fields or CWC on the Web?

How do I handle computed fields or CWC on the Web? I have a form and there is button that opens a pop-up window in which I fill in fields. When I close the window, the data goes to the form. It works fine with editable fields but not with C or CWC. I use JavaScript to take the data from the pop-up window. Do you have any examples of this working, or is it impossible?
It won't work if the fields are computed or computed when composed. The server will ignore the changes to those fields when they are re-submitted. The server only knows about the behavior of the form from what it can "see" in the design that's on the server.

There are a number of ways of overcoming this. One is by letting these fields be editable. Then add an attribute to the field that hides it when the browser users see it. You give it the attribute type='hidden'. In the Domino Designer, in the list where you also put the default value and the input translation etc., there is a box for HTML Attributes. Put "type="hidden"" in that box to hide the field in the browser, but leaving it accessible and able to be modified to JavaScript.