The NPRs do consume fuel and have to produce it. They just don't suffer any penalty for being out of fuel except the overriding priority to refuel, so they will run out eventually.
Maybe I should modify minor races so that at some point they do develop jump capability, but not for several decades after creation.
Another option might be to have minor NPRs ignore the overriding priority for refuel, resupply, etc., either if they're out of fuel completely or at least reducing the priority of that order so they can effectively defend once they run out of resources. Since they are limited to a single system, the go-home-to-refuel behavior isn't as important from the perspective of simulation for the benefit of the player.
Another one can be every, let's say, two or three years the game regenerates minerals in the minor race system, and this triggers a (new) geosurvey to find them. This regeneration ends when the system is discovered by another race (the player or a NPRs), and the minor race can now discover/buy/steal the jump drive technology.