If you're familiar with MPE then just add Cloaking Device property and configure strenght, (dunno how this one works as I never noticed any difference between 1-100 strenght factor) placement
etc.
If you're not familiar with it then open any Klingon/Romulan ship hardpoint and copy whole property as well as a line on the bottom of the HP which enables new feature, it's important to change property name as it most likely be made for let's say Bop.Cloaking.Device so you have to change it to Constitution(or whatever it's called on the rest of HP properties).Cloaking.Device.
of course it's alot easier to add it through MPE ;)