Fill the holes with crumpled up newspapers to keep the mortar from falling down deep inside. The trowel on a layer of mortar over the blocks, filling in the holes and forming a slope away from the house. So at the narrower blocks have it come up an inch or so and taper it down to nothing at the edge of the lower blocks. That way it will shed water away from the house. You can also build up the earth around your house with it sloping away from the house to keep rainwater out of your crawlspace.