CONTROL PAGES
in the outline view on the left side of the home windowNew…
button at the top of the windowLink to External URL
on the Client action
popup and insert the following):/editvarpage?name=SOME_VARIABLE_NAME&redirectPage=RETURN_PAGE_NAME
replacing the stuff in all caps with the appropriate information. Remember, if there is a space in the control page name, substitute it with “%20” (i.e. if your control page name is “My House”, you'd enter My%20House.
There is also a plug-in that will allow you to do this (if you're using a version prior to 4.0). Check out the IWS Variable Plug In in the File Library.