Strange mapping requirement

[mynkow]

I have two classes and mapping for the collection:

class User
{
    Guid ID;
    string Name;
}

class Group
{
    Guid ID;
    string Name;
    IList<User> Members;
}

// GroupMap
HasMany(x=>x.Members).Inverse().Cascade.AllDeleteOrhpan().etc.

This one works. When I add a User to the Members collection NHibernate cascades the operation. Same for deletes and updates.

Now I want to change my model a bit and this will change also the mapping. The collection is IList<Guid>. What I really want is the cascade to remain. That means that I have to do some custom persister or IUserType. The mapping should tell the object type like HasMany(x=>x.Members) and the collection will hold the IDs

class User
{
    Guid ID;
    string Name;
}

class Group
{
    Guid ID;
    string Name;
    IList<Guid> Members;
}

// GroupMap
HasMany<User>(x=>x.Members).Inverse().Cascade.AllDeleteOrhpan().etc.

Any ideas where can I start from? I think that there is no out of the box solution but who knows...

PS: This is cross post: http://stackoverflow.com/questions/11074610/strange-mapping-requirement