You can substitue a bit of salsa (thick and chunky) for the sweet pickle relish, 1/2 the onion, and shortning. Also, there is a LOT of sodium in the mustard, ketchup, vinegar, salsa, and Worcestershire sauce so you can skip the salt and substitute celery seed for the celery salt. You'll just want to let it sit for a few minutes and stir again before use.

Lastly, while this recipe is awesome, you can also use a tiny bit of olive oil to start cooking the onion, then add the hamburger to it until they're both done.