Strange it may seem but this is what I figured out for now if you navigate to https://bitcointalk.org/index.php you will still get 503 error. However if you navigate to to any other page or only https://bitcointalk.org/ it bypasses Cloudflare
Unfortunately I'm getting a 503 on https://bitcointalk.org/index.php?action=login2;ccode=... which makes it impossible for the parser to log in. But at least it's something I can experiment with and see if tweaking some parameters would help.