dynamic url based proxy redirect

[Renjith T <renjith.tom85@xxxxxxxxx>]

For a particular use case of ours - we are looking a scenario, where if 
the url matches a particular pattern 
http://myproxy.mysite.com/a/<rest_of_uri> , we would like to route the 
traffic to a given set of proxies behind the scenes, (and similarly, a 
different set of proxies for a different site pattern as well).

Let me know if / how that is possible, in terms of squid conf. to begin 
with. Thanks !