You can easily add such hyperlink using a delimiter field then adding a unique substitution such as the following to generate dynamic links.
[code:1]
<a href="
www.invalid.com/code.php?user=[user_id]">Sample Link</a>
[/code:1]
The substitution [user_id] will append the actual users User ID to the URL. Substitutions for any user field are available as well as much more; please see tutorials in signature for substitution usage.
Additional you could manually enter the URLs on a user by user basis using a Web Address field that is set to Read Only (so users can't edit it).