Blind Capture of Contact Email Address via UTM

We're currently transitioning from Eloqua to Marketo and I'm stumped on how to recreate functionality in Marketo that we have used in the past with Eloqua. I have outlined the scenario below:

We regularly survey our clients and use a UTM code to capture who is replying to the survey. This saves us from adding the self identifier fields within the survey and therefore saves our clients time. We used to do this in Eloqua by using this code 

Email=~~eloqua..type--emailfield..syntax--EmailAddress..innerText--EmailAddress..encodeFor--url~~

at the end of the survey URL and then had it feed to a hidden field in the survey. 

I cannot for the life of me find a similar code to map into a URL to use in an email in Marketo. Is anyone familiar with this? Do you know the code we should use to do this? 

Thank in advance for the feedback! 

Dani