To echo and add to Dale's comments, I would not add the molasses until secondary fermentation (I know, I know...). I would keep it to a light amount, personally - 4 ounces or less per five gallons.
Increasing the mash temp (as Dale suggested) would work best if you are just looking for a little residual sweetness, not necessarily a molasses flavor.
Other than that, DON'T add spices at the beginning of your boil...it will drain the flavor and aroma and leave you with a nasty bitterness that does NOT go away!!
I would add them in two separate additions, myself...first at about 10-15 left in the boil and one more at flame-out.
The first would be more for flavor and the second would be more for aroma.