Previous replies have confused PHP Switcher with PHP Selector.
PHP Switcher does/did work with the standard/free version of CWP.
If I find time, I'll check with one of my other instances - it already works with one...
EDIT: Running now.
Did you select appropriate PHP modules, then click Save & Build?
You should see this:
> PHP Compiler Started in Background. You can monitor PHP rebuild from the console using command: tail -f /var/log/php-rebuild.log
What particular version of PHP are you trying to use? Try 5.2.39 and/or 'latest' - works fine for me.
(CWP version: 0.9.8.924)