Sorry but I try to avoid query string params in mojoPortal cms features because they may live on a page with other features. One could have multiple contact forms on the same page even so relying on query string params on cms pages is problematic and can get very messy. It works fine for feature specific supporting pages (like the forums where it links to forum specific pages that are not cms pages, it is ok to use query string params in that situation) but not for the part of the feature that plugs into a cms page. That part of the feature needs to play well with other things on the page and should not expect to have control over the url nor expect extra information being passed in the url.
Best,
Joe