You can make mobile builders, they can build anywhere in supply. Ships without forcefield immunity have to destroy the FF before they can get into it. Ships with forcefield immunity for movement just ignore them entirely. Mobile builders can also make turrets. And mines. They can build almost anything a station can.
Basically, if you want to delay ships, you put a forcefield over the wormhole leading in. If you want to stop ships, you need sufficient firepower to complement the shield.