I did this for a customer for webaccess.
To get this working we used a webaccess framework with shibboleth authentication and send the user a special link to the survey.
We have this across various sites and domains and open within our nhs network so I don't this using shibboleth authentication would work. Also I don't have the budget to purchase anything to do this we need to be able to do this within the current infrastructure.
Ideally I would like to be able to do this within Workspace as this is the direction we would like to go with self service but we need it so people don't have to login and also can access the page from a URL we send them.
for SelfService and WebAccess i could give you some assistance, but I don't want to post an official how to here, as this might be a backdoor to service desk.
You can use Frameworks with Shibboleth Authentication method, without having a Shibboleth authentication instance.
Send me an e-mail to fabian(DOT)schmidt(AT)magelan(DOT)net so I can e-mail you the how to.
This is exactly the same obstacle I have just come across... logged with support but I guess I know what the answer will be! lol