ACE, can't modify the url.
But it can send redirect.
So you could build 3 redirect rservers, and have ACE loadbalance between them.
rserver redirect HTTP-REDIRECT1
webhost-redirection http://real_server/1/index.html
inservice
rserver redirect HTTP-REDIRECT2
webhost-redirection http://real_server/2/index.html
inservice
rserver redirect HTTP-REDIRECT3
webhost-redirection http://real_server/3/index.html
inservice
serverfarm redirect SF_REDIRECT
rserver HTTP-REDIRECT1
inservice
rserver HTTP-REDIRECT2
inservice
rserver HTTP-REDIRECT3
inservice
But even if it works, this does not sound good.
It seems like a design done by an application server person who does not know how network loadbalancers work.
It seems like all you need is stickyness, which you are trying to achieve by redirecting to /1 or /2 or /3.
But this can be done differently with cookies or by just doing stickyness on source ip address.
Gilles.