Transparent load balancers exist and don't have the issues you are talking about.
Hardware or software? There's some hacks with TPROXY/HAproxy I've seen that would do the transparent proxy but the setup seems like more trouble than it's worth.
Re:SSL session caching in nginx
by ominous_prime on Monday June 27, 2011 @09:41PM
(#2703690)
IPVS is built-in to the Linux kernel, and HA projects like keepalived have ipvsadm integration. Tproxy works fine, and has been in the kernel since 2.6.30. In most load-balancing cases, losing the remote IP address isn't that big a deal (you have to deal with NAT too), and a full proxy like haproxy has it's benefits.
IMO (and I believe Google agrees - http://www.imperialviolet.org/2010/06/25/overclocking-ssl.ht...) the advantages of terminating SSL at the load balancer outweigh the horizontal scalability of this approach, at least in most cases.