I\'m using NHibernate HiLo as my identity generator. I currently have a sepperate table in my database for each of my entity tables. For example I have Customer and CustomerKey
I have written about this here: http://daniel.wertheim.se/2011/03/08/nhibernate-custom-id-generator/
there is a patch for adding this on JIRA, but I don't know when it will be in the trunk https://nhibernate.jira.com/browse/NH-1374
Have you tried using the where property of the hilo generator? Something like:
<class name="Customer">
<id name="Id">
<generator class="hilo">
<param name="where">TableName = 'Customer'</param>
...
</generator>
</id>
...
</class>