Use Post as Front Page

You just need to modify the main query:

// inside functions.php
function wpse47667_intercept_main_query( $wp )
{
    // Modify the main query object
    $wp->query_vars['custom_tax_name'] = 'custom_term_slug';

    return $wp;
}
add_filter( 'parse_request', 'wpse47667_intercept_main_query' );