CodeIgniter htaccess for subdomain without changing URL - apache

Question

I have been searching this but could not find the answer. I might have missed something here. Basically I have two applications under one CI installation. Each of the app will have their own subdomain. So for example http://foo.example.com/ which will redirect to http://example.com/foo and http://bar.example.com/ which will redirect to http://example.com/bar. The http://example.com/ itself will be some kind of a landing page.
The redirect part is working fine. But it keeps changing the URL from http://foo.example.com/ to http://example.com/foo, which I want to prevent. I have read a solution to use a [P] instead of [L] flag, but that will require me to enable proxy.
Is there any other option for me to do this other than enabling proxy?
Currently my htaccess file is as below:
RewriteEngine On
RewriteBase /
#Removes access to the system folder by users.
#Additionally this will allow you to create a System.php controller,
#previously this would not have been possible.
#'system' can be replaced if you have renamed your system folder.
RewriteCond %{REQUEST_URI} ^system.*
RewriteRule ^(.*)$ /index.php/$1 [L]
#Checks to see if the user is attempting to access a valid file,
#such as an image or css document, if this isn't true it sends the
#request to index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]
# The line for subdomain
RewriteCond %{HTTP_HOST} ^(.*)\.example\.com
RewriteRule ^(.*)$ http://example.com/%1/$1 [L,NC,QSA]
# If we don't have mod_rewrite installed, all 404's
# can be sent to index.php, and everything works as normal.
# Submitted by: ElliotHaughin
ErrorDocument 404 /index.php
Thank you very much for the response.