since you are doing ssl termination you can do cookie sticky and have the ace either learn a cookie from the server or insert a cookie to provide sticky.

for instance to do cookie insert

sticky http-cookie COOKIE1 GROUP3

cookie insert browser-expire <-- this makes it a session based cookie. If you want the cookie to expire at a set time you can leave off browser-expire 

and then set a timeout . the timeout is not on ace rather we will send a utc expire time to the browser

serverfarm test

then call the sticky serverfarm in your load balance policy

policy-map type loadbalance first-match L7PLBSF_STICKY-COOKIE_POLICY

  class class-default

    sticky-serverfarm GROUP3

you can also use other sticky methods see

http://www.cisco.com/en/US/customer/docs/interfaces_modules/services_modules/ace/v3.00_A2/configuration/slb/guide/sticky.html#wp1070365