Matt, I don't know what the certificate gateway thing is, but if you get rid of that and do the following, you can get the dependancy issue solved:
In the settings for the quiz, where you set the dependancy of 80% there is a feedback field, go to the page that shows you your certificate and copy the URL, then paste it in the feedback filed. You need to add a bit of html to exclude the link and insert the word certificate:file.php/3/link.html>Post-Course Survey
You will need to instruct your audience to look for the feedback link to the certificate. Also, make sure you have general feedback checked in the settings for the activity you are setting as the gateway to the certificate. The only issue I am having with tis method is that it doesn't allow you to hide the certificate link.