In order to use two keys/MLSs in our WordPress plugin you need to have a WordPress multi-site setup.

A WordPress multi-site allows you to share plugins and themes. This will allow you to enter a different key and secret for each site under the WordPress network setup…
http://codex.wordpress.org/Create_A_Network


After a multi-site is setup

First, you need to make sure the plugin is enabled for the network. This will be under My Sites>Network Admin>Plugins. If the flexmls® IDX plugin is not activated for the network, there will be a link under the plugin title “Network Activate”. If it is already activated for the network the link will say “Network Deactivate”.

Second, edit the site you wish to add the second MLS to – From the Network Admin dashboard this is under the Sites menu option. There should be an edit option under each site you have. Once you are editing the site, go to Settings>flexmls IDX, here you should be able to enter the API key and secret for the second MLS and click Save Settings.