How do I write a custom validation method with parameters for my ActiveRecord model?

In my model I have:

validate :my_custom_validation

def my_custom_validation
 errors.add_to_base("error message") if condition.exists?
end

I would like to add some parameters to mycustomer vaildation like so:

validate :my_custom_validation, :parameter1 => x, :parameter2 => y

How do I write the mycustomvalidation function to account for parameters?