Howdy.
If Disqus requires redirects, and you require Disqus, then that's probably the best you'll be able to do. You mentioned that you reached out to their support team; they'd be able to provide more help on the issue than we will.
You can make several other straightforward optimizations for your site though. Making your 3rd party scripts asynchronous and optimizing your images should both be easy and straightforward wins.
On the whole, your site seems to be doing pretty well. You have lots of little nits to pick off, but a score of 90 indicates that the savings will be modest.
Please let us know if you have any other questions.