Customize a single survey based on URL

I have a survey use for academic research purposes. My first 'question' is actually descriptive text that explains the subjects rights and protections as dictated by my IRB.
I am required to show some subjects one description and other subjects a different description.
The simple way of doing this would be to copy the survey and send out two different surveys. However. I would prefer to have a single set of questions to administer and a single database/result set.
What I would like to do is to be able to have two URLs that feed to the same survey. If the URL contains &user=2 then I would show the alternate description. Is there a way to do this? I looked at skip logic and it didn't look like it could vary based on URL. I don't want the subject to need to do anything special because they will not know if they are in set one or set two.
Thanks,
Michael