This is a late reply, but this post has had 130 Views at present, so an answer might still prove useful to someone else.
There are three resources that I would advise:
1) QlikView Mashups - Simple Document Integration in order to get an idea of what is possible
2) Passing Parameters in a URL and Document Chaining to see a working example of the concept, as well as, document chaining
3) In order to pass a variable value as a parameter @Andy Hyde suggests that you go to C:\Program Files\QlikView\Server\QlikViewClients\QlikViewAjax and "add a line to the opendoc.html file", e.g.
var d1 = Qva.ExtractProperty("param1", null);
var d2 = Qva.ExtractProperty("param2", null);
For more, check out How to transfer parameter in url? I use opendoc.htm to open a ajax client.