I realize this post is a year or more old, but the way I was taught to make Mexican rice is different from the way I learned to make "southern" white rice.
The reason Mexican rice doesn't clump is that it is browned in oil FIRST. Not sure how it's done in restaurant quantities, but at home, preparing 1-2 cups, I brown in a skillet first. Then I had the tomatoes and hot water and stir. Unlike white rice (which is added to boiling water, where you cover, simmer, turn off, allow to rest 5 minutes), I add the expected amount of water (2 cups per 1 cup rice), but I have leeway to add more, if necessary.

To this day, I haven't figured out how to do what you are wanting to do with white rice. I was an amazing buffet that I got to every few months with fellow musicians... I asked the cook, who was at the buffet giving instructions to another guy and he said "it's a secret". LOL!