Well technically you can do this in these zones (as shown in HWS 3,4,5).
But these Zones are really reserved for the Elemental Garage ships and any other would get removed.
We will setup player driven sell zones with the 7th july patch.
However it is bit more tricky since these ships you sell have to be logically in PvE and PvE parking playfields are normally taxed. So you have to decide if you want to do it or set the price higher regarding that.
Giving random selling zones everywhere is a ton of work, therefore it is included in the NPC Trader donation option.
We will see - maybe there is an even better way later.