Removing the URI before using the pool

We are running BIGIP version 4.x and I have the following requirement and can't seem to get it to work.

 

Users type in http://manu.mapleleaf.ca/mcf, the /mcf will be tested in the rule and the rule is.

 

if (findstr(http_uri, "/", 1, 3) == "mcf") {

 

use pool MANU_MCF

 

}

 

else {

 

discard

 

}

 

 

The thing is when the URL is passed to the pool I need the /mcf removed because it is the default site for the port.