Multiple web site redirection

Hi all,

I apologise if this is not the right place to ask this;

I have two web servers, both serving a multitude of different sites and 
domains, both HTTP and HTTPS.  Lets call them 1.1.1.1 and 1.1.1.2.

We're leaving the hosting provider where they live, and they being 
migrated to two identical servers at another, lets say 2.1.1.1 and 2.1.1.2.

Each server has around 8 additional IPs where the SSL sites are bound.

As we don't control the DNS for the majority of these, it seems unlikely 
that I can get dozens of clients to change TTL and A records at the same 
time.  I don't want them both to be live in parallel, and I don't want 
to migrate site by site and take the next millennium to complete the 
migration.

I've considered using squid or apache to proxy the requests from the old 
host to the new, but I haven't managed to make this work.  All the 
examples seem to assume that everything is HTTP and its a local accelerator.

I am currently thinking about iptables and NAT to accomplish the same 
thing, just simply redirecting the IPs to the new range.

What are thoughts about the best way to accomplish this?

Thanks in advance,

Craig Reynolds