find_by_sql returns Strings! How to I type cast?

When i run find_by_sql the extra fields not in the Model are returned
as Strings.

What is the correct way to convert all the extra fields to their correct
type? Is there a way to somehow define these extra fields in the Model
class to ensure they will always be returned correctly? Or is their a
better method.

I will be using find_by_sql a lot so a clean solution would be good.
(I am using Mysql)s

Thanks in advance
Chri