If you do not wish to move your entire server to use alpha mode (or beta) but keep the mainline in stable, but still wish to install the actual package; you just
enter the information from channel and on and the plug in will install.
$:/var/www/magento$ ./pear install magento-community/Florent_Piwik Failed to download magento-community/Florent_Piwik within preferred state "stable", latest release is version 0.4, stability "alpha", use "channel://connect.magentocommerce.com/community/Florent_Piwik-0.4" to install install failed $/var/www/magento$ ./pear install channel://connect.magentocommerce.com/community/Florent_Piwik-0.4 downloading Florent_Piwik-0.4.tgz ... Starting to download Florent_Piwik-0.4.tgz (4,163 bytes) .....done: 4,163 bytes install ok: channel://connect.magentocommerce.com/community/Florent_Piwik-0.4