I never add all the salt at once, it adds so much better flavor if you add the salt throughout the cooking process. Plus, if you oversalt all at once you can numb your taste buds and you will more than likely add more salt than you intended.
If you do not want to use essential oils you can add minced ginger and lemongrass to the shallot mixture and puree in the soup and add more lime juice at the end. Easy!