Rewrite Portion of URI

This is what I have tried so far

when HTTP_REQUEST {
HTTP::uri [string map {"/*/Login.aspx?" "/app.web/APPvirtualDirectory/Login.aspx?"} [HTTP::uri]]
}

e.g.

 config

root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm virtual bar
ltm virtual bar {
    destination 172.28.24.10:80
    ip-protocol tcp
    mask 255.255.255.255
    pool foo
    profiles {
        http { }
        tcp { }
    }
    rules {
        myrule
    }
    source 0.0.0.0/0
    source-address-translation {
        type automap
    }
    vs-index 14
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm pool foo
ltm pool foo {
    members {
        200.200.200.101:80 {
            address 200.200.200.101
        }
    }
}
root@(ve11a)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm rule myrule
ltm rule myrule {
    when HTTP_REQUEST {
  if { [HTTP::uri] starts_with "/CUST_A/" } {
    HTTP::uri [string map {/CUST_A/ /app.web/APPvirtualDirectory/} [HTTP::uri]]
  }
  HTTP::header replace Host "www.mysite-new.com"
}
}

 test

[root@ve11a:Active:In Sync] config  ssldump -Aed -nni 0.0 port 80
New TCP connection 1: 172.28.24.1(39115) <-> 172.28.24.10(80)
1393145648.5634 (0.0029)  C>S
---------------------------------------------------------------
HEAD /CUST_A/Login.aspx?C=98620001&UN=COMS8365&PW=av99er89uj&F=EN HTTP/1.1
User-Agent: curl/7.15.5 (i686-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5
Accept: */*
Host: www.mysite-old.com

---------------------------------------------------------------

New TCP connection 2: 200.200.200.14(39115) <-> 200.200.200.101(80)
1393145648.5958 (0.0298)  C>S
---------------------------------------------------------------
HEAD /app.web/APPvirtualDirectory/Login.aspx?C=98620001&UN=COMS8365&PW=av99er89uj&F=EN HTTP/1.1
User-Agent: curl/7.15.5 (i686-redhat-linux-gnu) libcurl/7.15.5 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5
Accept: */*
Host: www.mysite-new.com

---------------------------------------------------------------

The issue I have is there are 100+ different virtual directories on the legacy web server and I don't currently have a complete list.

Is there a way to replace everything between / and / of the legacy URI with /app.web/APPvirtualDirectory/

For example...

/CUST_A/Login.aspx?C=98620001&UN=COMS8365&PW=av99er89uj&F=EN
becomes
/app.web/APPvirtualDirectory/Login.aspx?C=98620001&UN=COMS8365&PW=av99er89uj&F=EN
and
/CUST_ZZZ/Login.aspx?C=98620001&UN=COMS8365&PW=av99er89uj&F=EN
becomes
/app.web/APPvirtualDirectory/Login.aspx?C=98620001&UN=COMS8365&PW=av99er89uj&F=EN
...
...
...

I finally received the list of virtual directories from the development team.

This is what I ultimately used...

Create a new string Data Group containing the legacy URI

ltm data-group legacy_uri
  records {
    /custa/
    /custb/
    /custc/
    ...

iRule

when HTTP_REQUEST
  if { [class match [string tolower [HTTP::uri]] starts_with legacy_uri]} {
  set uri_leg [class match -name -- [string tolower [HTTP::uri]] starts_with legacy_uri]
  set uri_new "/app.web/APPvirtualDirectory/"
  HTTP::uri [string map [list $uri_leg $uri_new] [string tolower [HTTP::uri]]]
  }
}

Is this the best way to go about this or is there a more efficient method?

This can be fixed with some URL rewrite rules on most Web servers at the backend, where this should be done.