You can add one class to the Addmappings
from the assembly that it belongs to.
My config is like this:-
mapper.AddMappings(typeof(CmsMeta).Assembly.GetTypes());
Basically I have 50 or so mapping classes but only need to specify the assembly where one of them lives. NHibernate will auto scan that assembly to find the rest. All my mapping and model classes live in a single separate assembly Domain.Model