Depending on where the latch broke, you will either need a flashlight and a piece of stiff wire, or a trip to the dealer.

If you shape the wire into a little hook (may take some fiddling with pliers to get it the right size to fit inbetween the grille slats), and look into the grille, you should be able to see what's left of the hood latch. The latch handle forks into two arms near where it attaches to the latch itself. If the handle has broken off BEFORE the point where the two arms are molded together, you have yourself a nice place to hook the wire onto. If the handle has broken off PAST the point, and there are just two arms hanging aimlessly into the void, you may be able to hook onto an appropriate part of the latch itself (never tried this myself), or otherwise find some way of attacking it from underneath...

-anthony