iRule to match on the URL and then perform encryption and send traffic to designated web servers

This shouldn't be a problem. Have a look here for some of your options: http://devcentral.f5.com/Default.aspx?tabid=53&view=topic&postid=14536

In particular, look at hoolio's first example which shows you how to selectively disable ssl (you can just as easily *enable* it as well) based on uri:

 
  Pasted from http://devcentral.f5.com/Default.aspx?tabid=53&view=topic&postid=14536 
 when HTTP_REQUEST { 
  
     Check if request matches the criteria to disable server-side SSL 
    if { [HTTP::uri] starts_with "/clear"}{ 
  
        disable SSL on the serverside context 
       SSL::disable serverside 
  
        select the http pool 
       pool http_pool 
  
    } else { 
        default is to use server-side SSL and the https pool 
       pool https_pool 
    } 
 } 
 

Be sure and read the whole thread as it's got a bunch of good stuff in it and it'll give you a feel for some of the options available to you.

-Matt