I assume by narrowing you actually mean the arms have been shortened for a different track width?
If the narrowing hasn't gone too far, the easiest method would be to shorten the inner ball socket shaft by the same amount and rethread the ends. You might even have to find a shorter ball socket from another vehicle.
But you have to pay attention that you do not alter the swing relationsip between the lower control arm and the tie rod assembly as it will lead to bump steer. There are products that will eliminate bump steer if the two swing arcs are not the same.