Can command or option and shift (just those two keys) be assigned as an OS X shortcut?
You can use KeyRemap4MacBook. This inserts Q when releasing shift:

&lt;autogen&gt;__KeyOverlaidModifier__ KeyCode::SHIFT_L, ModifierFlag::OPTION_L | ModifierFlag::SHIFT_L | ModifierFlag::NONE, KeyCode::SHIFT_L, ModifierFlag::OPTION_L, KeyCode::Q&lt;/autogen&gt;
&lt;autogen&gt;__KeyOverlaidModifier__ KeyCode::SHIFT_R, ModifierFlag::OPTION_R | ModifierFlag::SHIFT_R | ModifierFlag::NONE, KeyCode::SHIFT_R, ModifierFlag::OPTION_R, KeyCode::Q&lt;/autogen&gt;


This inserts Q when pressing shift, but it requires pressing shift before option for shortcuts like ⌥⇧[:

&lt;autogen&gt;__KeyToKey__ KeyCode::SHIFT_L | ModifierFlag::SHIFT_L | ModifierFlag::OPTION_L | ModifierFlag::NONE, KeyCode::Q&lt;/autogen&gt;
&lt;autogen&gt;__KeyToKey__ KeyCode::SHIFT_R | ModifierFlag::SHIFT_R | ModifierFlag::OPTION_R | ModifierFlag::NONE, KeyCode::Q&lt;/autogen&gt;


This remaps pressing option and shift simultaneously:

&lt;autogen&gt;__SimultaneousKeyPresses__ KeyCode::OPTION_L, KeyCode::SHIFT_L, KeyCode::Q&lt;/autogen&gt;
&lt;autogen&gt;__SimultaneousKeyPresses__ KeyCode::OPTION_R, KeyCode::SHIFT_R, KeyCode::Q&lt;/autogen&gt;


See the source for the key code values and predefined settings.