How about this:
- Put chipmixer.com behind Cloudflare, with only a landing page.
- The landing page shows a link to Tor browser, .onion URL and a link to a (newly created) clearnet URL without Cloudflare.
- The URL without Cloudflare can be for instance nocloudflare.chipmixer.com. If there's no DDOS, it's available. During DDOS, the landing page is still available to point towards the .onion site.
- This way, Cloudflare only knows you visited the clearnet landing page.
Chipmixer's coffers must be flowing with cash so assuming they got an easy offramp that can take hundreds of dollars per month, they can probably afford to buffer with Akamai or Fastly instead.