Sort of untested, but give it a try.
Open ./sources/action_public/topics.php
Find:
if ( strstr( ",{$poll_data['result_permission']},", $this->ipsclass->member['mgroup'] )
OR $this->ipsclass->member['is_mod'] OR $this->ipsclass->member['g_is_supmod'] OR $this->ipsclass->member['g_access_cp'] OR $poll_data['result_permission'] == 'all' )
Replace with:
if ( strstr( ",{$poll_data['result_permission']},", $this->ipsclass->member['mgroup'] ) OR $poll_data['result_permission'] == 'all' )
Save and upload
Open ./sources/classes/post/class_post_new.php and ./sources/classes/post/class_post_edit.php (Same edit in both files)
Find:
$this->ipsclass->DB->build_query( array( 'select' => 'g_id, g_title', 'from' => 'groups', 'where' => 'g_is_supmod=0 AND g_access_cp=0' ) );
Replace with:
$this->ipsclass->DB->build_query( array( 'select' => 'g_id, g_title', 'from' => 'groups' ) );
Save and upload