do you host your own domain? o.o
just use the DNS-Server of your service, you bought the Domain.
so you just have to point the a-record to your proxy-ip (so in this example 5.6.7.8)
delete the ns1 and ns2 that point to your server (1.2.3.4)
make sure, your website is acessable via your ip (1.2.3.4), so the proxy will work.
edit
or do it like serverpolice said.
just use the DNS-Server of your service, you bought the Domain.
so you just have to point the a-record to your proxy-ip (so in this example 5.6.7.8)
delete the ns1 and ns2 that point to your server (1.2.3.4)
make sure, your website is acessable via your ip (1.2.3.4), so the proxy will work.
edit
or do it like serverpolice said.