Alcohol is first metabolized to acetaldehyde, then to acetic acid.  Most of the hangover effects are caused by acetaldehyde, close cousin to formaldehyde.  Drinking alcohol in large quantities leads to a decrease in the enzyme needed to convert acetaldehyde to acetic acid, which is harmless.  Vitamin B1 (thiamine) helps the body to maintain adequate levels of this enzyme (i.e. acetaldehyde dehydrogenase).  Taking 50 mg of thiamine before drinking and another before bedtime will cut down the severity of the hangover immensely.

Alcohol is also metabolized at a fixed rate.  Drinking twice as much means it will take twice as long to metabolize it.  There is no way to increase the rate at which it is metabolized.