Karabiner ( KeyRemap4MacBook) Ctrl to Command, preserve Ctrl+Tab and Command+Tab
Since both right and left ⌘ are identical in functionality (I hope this is the case in your setup), we first map left Ctrl to the right ⌘:

&lt;autogen&gt;
  __KeyToKey__
  KeyCode::CONTROL_L,
  KeyCode::COMMAND_R
&lt;/autogen&gt;


Then map right ⌘+Tab to Ctrl+Tab:

&lt;autogen&gt;
  __KeyToKey__
  KeyCode::TAB, ModifierFlag::COMMAND_R,
  KeyCode::TAB, ModifierFlag::CONTROL_L
&lt;/autogen&gt;