I'm not sure what this "hidden" is about, but Bobboau did something like that for us, and it should be already in CVS. I assume this "hidden" doesn't work anymore, otherwise you wouldn't have posted this
For Bob's method, just model the subsystems as usual, then give the submodel (in this example "fighter01") in the pof-file the following entry :
$special=subsystem
$nontargetable
In the ships.tbl do the following entry :
$Subsystem: fighter01, 1, 0.0
+non-targetable
This creates in this example a parked fighter on a flight-deck, which can be destroyed, but not targeted.
I have to admit, the pof-data entry was from the time Bob developed that, the table-entry came later. I'm currently not 100% sure, the "$nontargetable" in the pof-data is still necessary.
Starman©