You can't force his head back or his jaw open during the seizure. You have to stay clear and wait for the erratic and violent movements to stop. Don't try to block his flailing arms or legs neither, both of you can be injured by trying so. -DeSelys
You need to monitor the airway during seizures. If there is an airway present, you don't have to do anything - providing the immediate environment is safe. If there is no airway, you need to help the victim right away. It is as easy as tilting the head back.
EMERGENCY FIRST-AID TREATMENT
* Protect the person from injury. Clear the area of furniture or other objects that may cause injury from falls during the seizure.
* Do not attempt to force a hard object (such as a spoon, or a tongue depressor, etc.) between the teeth. You can cause more damage than you can prevent by doing this!
* Do not attempt to restrain or hold the person down during the seizure.
* Protect the person from inhaling vomit or mucus. Turn the person to the side if vomiting occurs. Keep the person on his or her side while sleeping after the seizure is over.
* If the person having a seizure turns blue or stops breathing, try to position the head to prevent the tongue from obstructing the airway. Breathing usually starts on its own once the seizure is over.
* CPR or mouth-to-mouth breathing is rarely needed after seizures and cannot be performed during the seizure.
* Repeated or prolonged seizures without regaining consciousness or returning to normal behavior between them (status epilepticus) may cause severe lack of oxygen in the body. This an emergency situation requiring immediate professional assistance!
http://www.nlm.nih.gov/medlineplus/ency/article/000695.htm