As a general rule, batteries should never be left inside the laser for a prolonged period of time. There is a risk that the battery may start to leak and damage the laser.
Here are two possible solutions:
1) Drive a long, sharp tipped screw into the end of the battery and tie a string on it to pull the battery out.
2) Chill the laser in a fridge for several hours, heat up the battery area and end quickly with a hair drier or heat gun and the laser should expand quicker than the batteries. Hopefully he can then dislodge it with a small screwdriver.