Anthonyb is right.
This is "wire coat hanger" territory here! You can fish around until you can get ahold of the latch, but patience is your friend.
This happened to me accidentally on the ML. Was installing a bug shield and it required temporarily removing the catch on the front of the grille. Needless to say, during installation, SLAM! Hood is shut and I can't get to the latch to open it!
Out came the coat hanger, and 30 minutes later, I was back in business.
A flashlight would help as well...