I did something like this. Posted results in another thread:
So far, the pineapple in mine is really strong and sour. From what I've read on GotMead and this site, pineapple takes a little time to settle down. After I let mine age a bit, I may go back and add some coconut flavoring (maybe make an extract). Using rum and molasses is a neat idea. I think I might add a little buckwheat honey to mine (to me, buckwheat honey tastes similar to molasses).
One note: You may not need much nutrient with pineapple. I added none to mine, and the fermentation was nearly explosive. Had I done my primary in a carboy, I would have had quite the mess.