there is currently no option for that, but maybe nice idea for v2.6.2+ will have a look on that...
**edit**
Ok, implemented in v2.6.2+
Who wants this in v2.6.1+, open /admincp/arcade.php
search for
Code:
print_select_row($ibforums->lang['acp_main_g_display_sort'], 'g_display_sort', array('gtitle' => $ibforums->lang['acp_alphabetic'], 'gcount' => $ibforums->lang['acp_oftenplayed'], 'position' => $ibforums->lang['acp_userdefined']), $arcade['g_display_sort']);
and replace with
Code:
print_select_row($ibforums->lang['acp_main_g_display_sort'], 'g_display_sort', array('gtitle' => $ibforums->lang['acp_alphabetic'], 'gcount' => $ibforums->lang['acp_oftenplayed'], 'added' => $ibforums->lang['dateadded'], 'position' => $ibforums->lang['acp_userdefined']), $arcade['g_display_sort']);
After this you can select it in the default sort options (arcade main settings)