You could also implement the "hook_views_pre_view" function in order to alter the contextual filter arguments of your view and display. In order to add multiple taxonomy values for the same argument, you can change the $args[0] element from the $args variable of the hook.<br>
For example: $args[0] = '22+14+64';<br>
Remember to check the "Allow multiple values" option of the contextual filter.