How do I get appended data from a URL into a Brio variable.

[Jameson1979]

I need to populate a variable in my Brio query, with a value passed in a URL using an EIS. eg.

http://myserver/Accounts/Accounts_Query.bqy?AccountNumber=12345

- I need to set 12345 as the variable.
I've been trying all variations of "var MyURL = ActiveDocument.URL" but all this keeps setting my variable equal to "

http://myserver/Accounts"

How do I get my EIS to pick up the rest of my URL?
My query is located on a dedicated on-demand Brio Server! Could this be part of the problem?
Any help is most appreciated.
Thanks in advance.