Only thing I can think of is http header-insertion. Create an action-list, that inserts the original client src.ip/port into the http-header. The configuration is quite simple:

action-list type modify http name

  header insert both Host header-value %is:%ps

Then apply the action-list to your loadbalance policy-map.

Take a look at the url below for futher information:

http://www.cisco.com/en/US/docs/app_ntwk_services/data_center_app_services/ace_appliances/vA3_1_0/configuration/slb/guide/classlb.html#wp1131842

But that depends on your situation. If is the original client src.ip/port is expected in the L3/L4 header, this won't cut it. Is this for logging purposes or some form of packet filtering ?

If you intend to run your ACE in one-arm mode, in my opponion, src.nat and header-insertion is your only option.

hth

/Ulrich