I can't stand either rum or boba, but my experience with cooking grains of stuff (rice, oatmeal, barley) in stuff other than water. Well, including some water, but not JUST water. Broth, milk, juice, etc. They don't have such a drastic boiling point difference as rum, but I've found they're all much better for flavoring grain than for cooking it to the right texture. It's a significant trade-off, and I have not found a way around it by adjusting the cooking time or temperature...the only way I can get good texture is to dilute the flavored liquid or do some pre-cooking in plain water.