Comment 6 for bug 635934

OK I think I have a general workaround which is not (too) ugly.

<Connection>
  <ConfigKey>[Channel1],cue_set</ConfigKey>
  <EmitOnDownPress>true</EmitOnDownPress>
  <ButtonState>RightButton</ButtonState>
  <ConnectValueToWidget>false</ConnectValueToWidget> <!-- fixes play/pause button state bug -->
  <ConnectValueFromWidget>true</ConnectValueFromWidget> <!-- not required since it defaults true -->
  <PushButton>true</PushButton> <-- used to force WPushButton to treat this connection like a pushbutton -->
</Connection>

It will be an error to connect two controls to RightButton (or LeftButton) with different PushButton values.