I wrote a NHibernateDataSource, which can be used in ASP.NET web forms applications just like their counterparts EntityDataSource and LinqDataSource.
It requires a LINQ to NHibernate NHibernateContext-derived class which specifies the queryable entities. You can get it from the NHContrib site.
I have used code from Microsoft's LINQ samples, of which I talked about on a previous post, and you can get a precompiled assembly from there.
I have not implemented the InsertParameters, DeleteParameters and UpdateParameters properties, only the WhereParameters, but it shouldn't be too difficult.
Please note that this code is merely a proof of concept, it may have problems, and it is not optimized. If you find anything in it that should be improved, drop me a line. As usual, hope you find it useful!