--- ./app/code/core/Mage/Catalog/Block/Product/List/Toolbar.php	2011-03-25 14:04:29.000000000 +0100
+++ ./app/code/local/Mage/Catalog/Block/Product/List/Toolbar.php	2011-03-25 14:04:16.000000000 +0100
@@ -353,6 +353,11 @@
      */
     public function getCurrentDirection()
     {
+        // add static direction for some sort by
+        if ($this->getCurrentOrder() == 'your_attribute') {
+            return 'asc';
+        }
+
         $dir = $this->_getData('_current_grid_direction');
         if ($dir) {
             return $dir;