javascript - How can I enable scrolling only for a parent window using window.showModelessDialog() in IE7 without jQuery?

Question

I want JavaScript to open a popup to modifying data for certain rows which have been selected via checkboxes. The rows exist in the parent window.

I am having trouble enabling only the scroll control in the parent window. I am currently using window.showModelessDialog(), which enables all of the parent controls. I only need the scroll.

My app is intended to work on IE7, and I cannot use jQuery.