Cloudflare runs a free IPv6 to IPv4 proxy with their service. Cloudflare's CDN normally works on a reverse proxy (you publicly see a Cloudflare IP for your site, while it proxies your actual IP to load your site).
1) Signup for a free account at Cloudflare.com and add your domain (you can add as many as you want)
2) Update your domain's name servers at your registrar to the ones Cloudflare supplies (<name>.ns.cloudflare.com)
3) Edit your Cloudflare DNS records, create & point your domain/subdomain's quad-A (AAAA) record to one of your LES IPv6 Addresses (see your welcome email with your VPS info)
4) Make sure you have "Cloudflare On" for the domain/subdomain record you just setup (make sure the little cloud icon is orange next to the record)
5) Head into your "Cloudflare Settings" for your domain - select the gear icon next to your domain in the main domain list
6) Scroll down and under 'Automatic IPv6' change the default mode 'Safe' to 'Full'
7) Modify your web server to listen on the IPv6 address you used above, on port 80 of course