I am attempting to get nhibernate working in medium-trust. What I found said that I needed to use a proxy generator. I pulled the one from nhibernate's site. When I attempt to use it, I recieve an error that it could not load the assembly 'DynamicProxyGenAssembly2'. Is there something I am missing or is there one that works somewhere. I would prefer not to use the generator, but there seems to be no alternative with nhibernate.
From what I gather the issue with medium trust is the use of reflection being nerfed some what (though I could be completely off here).
It also seems that your approach of physically pre-building the proxy objects seems to be the suggested one and this link may help.
To be honest I had a similar issue with shared hosting and decided to opt for using a a hosting provider that offered virtual server. This obviously removes the medium trust issue as it's like having a cheap and nasty dedicated server at your disposal.
I know that this answer may not have been the best, but I do feel your pain and wanted to chime up a little. Also, its worth mentioning that the best place to get NHibernate related questions answered is their forums (http://forum.hibernate.org).