It takes roughly 2.8 seconds for a grenade to explode once the grenade has stopped moving. Simply delete the grenade before the time is up:
PHP Code:
getGrenadeOrigin()
{
// delay finding the grenade's origin until it lands
self waitTillNotMoving()
// this is the origin you want - do what you want with it from here
origin = self.origin;
wait( 1.8 );
if( isDefined( self ) ) self delete();
}