A friend of mine suggested putting some bricks in the holes and then concreting.
That would work, but you need "mortar" instead of conrete.
The difference is concrete has rocks in it, and mortar doesn't
The easiest way to mix it would be to get a "mixing tub" from Home Depot, Lowe's, etc, and a small masonry trowel.
Google (Search Results)
Mix the mortar with just enough water so it's about the consistancy of mashed potatoes, and use the trowel to put about an inch in the bottom of the opening, a little wider than your brick, then lay a brick lengthwise in the mortar, pushing it down a little to set it in.
Keep the end of the brick back from the edge of the opening about 1/2 to 1 inch.
Fill in around and on top of the brick with more mortar, or pieces of brick and repeat the process with more bricks. Don't worry about how it looks as long as the openings are sealed.
When you get near the top you may have to use pieces of brick to fill in odd spots.
Once you get it closed off, use the trowel to throw mortar onto the ends of the brick to fill up the gap at the end, and then smooth it off evenly.
When its nearly set, you can brush it with a paint brush and some water to get a very smooth finish
Take your time and it won't be as complicated as it sounds