Rethink the approach. Here's another way.
I think it would be easy (easier) to just show a particular Link to any particular logged in User. Rather than worrying about a Redirect, just let 'em login and see a page on your site, with Conditionals or whatever to show different content to each User.
You can use getcurrentuserinfo to show a paragraph of content that is tailored to each user name. This isn't too mysterious for you, because you want to create the Usernames yourself, so you know which Username to conditional for.
For example, they log-in, they see a page on your site,
if username is "Jim"
Our Terms are: ____
Price Quote: $ ____
Other Info: ____
CLICK HERE TO SEE JIM'S WEBSITE DEMO IN ACTION
And of course have this hidden from anyone whose username is not "Jim" or "Admin"
Have "Admin" able to see them all, in a list on 1 page