I wouldn't turst your source as far as I could throw them. An Interceptor type ship:
Seeks out his enemies, or parks in orbit around a planet
if he can't find any. Buzzes incoming ships to scan them
for illegal cargo. Also acts as "piracy police" by
attacking any ship that fires on or attempts to board
another, non-enemy ship while the interceptor is
watching.
"Parks in orbit", from my observations, means sits on top of a spob waiting for another ship to enter the system. This doesn't sound like what you want.
Now, I seem to have accidently found a ship/govt combo that does something like what you want, at a big price. If a ship (with a trader type AI) has no fuel, and the govt of the dude that creates it has a very low tolerance for being outnumbered (try 0), it will try to run away. However, because it has no fuel, it can't enter hyperspace. So it sits right where it is, generally in open space near a planet (that's where the game places ships when it generates a system).
Unfortunately, this will probably only work in a system where the ship has enemies, although it seems to be possible to confuse the issue for the AI by making some-one in the system both an enemy AND an ally. Also, the ship cannot make a hyperjump, no matter what you do.