Hi Tom,
Sorry for taking so long to get back to you.
LinkTo feature can only be used with fields that belong to the list you connect to and pass the value of the field using the format <%FileName%>.
Your env. is more complex than that and therefore you could try to write some custom code base on the sample code we provide with our product (check QWP installation folder pleCode folder). Usign that project (check the documentation for more details) you can write you code to get the userID and then use that to redirect users to your link).