Alter persistence on HTTP1.1 headers

I am totally new to iRules and need help fulfilling a request. Currently, I have a VIP associated with a pool of 2 servers. The 2 servers both are identical and share the same info. The request is to use the default persistence of the VIP, except when a specific URL is sourced from the outside, (the servers are using host headers to differentiate the URLS) then once that specific URL is sourced, to use cookie persistence only for that URL. Any help would be greatly appreciated. Thanks.