Other than actually activating your core (and shooting for intensity over duration), the key to making planks not suck is to keep your mind busy, whether that's lifting limbs, walking around, or moving weights.
This exercise will hammer the trunk when you maintain a rigid plank. And once you've got that down, you can raise the difficulty by increasing the load or moving the weight in front of the hands.
You got the introduction to MRT last week, now here's the meat. If you've got limited time but want maximum results, this is your baby. The cool thing? The workouts won't take you much longer than 30 minutes.