Is your proxy spoofing client ip address ?
If yes, nothing special needs to be done.
If not, the problem is to sticky client to the same server.
We can't use sticky srcip because all traffic comes from a single ip.
The only solution is to use cookies.
You can use arrowpoint cookies.
You can find a sample config at :
http://www.cisco.com/en/US/products/hw/contnetw/ps789/products_tech_note09186a0080094398.shtml
Regards,
Gilles.