Not sure about a real work around because the ip address will still be ipv6 but will appear as ipv4 if you enable pseudo ipv4. You can replace ivp6 with ipv4 by setting the option pseudo ipv4 to either 'add header' or 'overwrite headers' (network > pseudo ipv4). It simply makes the ipv6 ip address (for people coming to your site through a VPN for example) an ipv4 address. I set mine to overwrite headers. It's a simple solution to allowing your visitors to always have a real ip address.
But as for a work around to actually stop ipv6, I'm not sure of a way.