Is there any way to pass a webapp item ID number to the input form of another webapp?

Context:

I'm working with a group of members who are collaborating on research.  The idea is for one person to post information, and then have others build on it, including attaching files, images and hyperlinks (so a simple forum doesn't work...).

If I could have the item ID from the main webapp be passed to the "child" webapp, all would be well.  I tried {tag_itemid} but of course, this didn't work.  I can display the item ID and have the users retype it into a form, but this isn't very streamlined...   Is there any way to pass the information directly to the form?

Thanks!!

Linda