If i set the constants described on http://contactform7.com/controlling-behavior-by-setting-constants/ in my theme's functions.php instead of wp-config.php, they don't seem to be picked up. I don't really like editing wp-config.php to define a plugin's behavior.
WPML has a similar constants (see ICL_DONT_LOAD_LANGUAGES_JS on http://wpml.org/documentation/support/wpml-coding-api/) which work fine when set in functions.php.
As a workaround, I created a plugin to set WPCF7_LOAD_JS and WPCF7_LOAD_CSS to false.
Best regards,
Thomas