[amibroker] Is there a way to exit unprofitable trades after a certain number of bars?

[trustdnb]

Is there a way to exit unprofitable trades after a certain number of
bars without using the CBT?  Essentially what I want is an Nbar stop
that only triggers on unprofitable trades, without stopping winners.

My weak attempt did not work:

Short = /*short fomula */;
ShortExit = BarsSince(Short) > 12 AND C >= ValueWhen(Short, C); 
Cover = ShortExit;