Q. re: Using models as join tables AND multiple models in forms

I read the section from AWDWR 2ed beginning at p. 337 about using a model to join tables. I'm trying to combine this concept with having multiple models on one form.

Let's say I have classes Account and Employee, with a many-to-many relationship between them. I don't want to use a pure join table because I want the AccountEmployee table to also contain a column for "role". (Actually, I will name the join table AccountEmployeeRelations)

I believe the model would look like this:

class Account < AR::Base
   has_many :account_employee_relations
   has_many :employees :through => :account_employee_relations

class Employee < AR::Base
   has_many :account_employee_relations
   has_many :accounts :through => :account_employee_relations

I assume I also need (but the book does not show):

class AccountEmployeeRelation < AR::Base
  belongs_to :accounts
  belongs_to :employees

In the migration for AccountEmployeeRelation I would guess I need lines like:
   t.column :account_id, :integer
   t.column :employee_id, :integer
   t.column :role, :string

The rest of my question probably depends on my interface. I guess I could first create an account, and then on a separate form assign employees to that account. I haven't tried that, but I would expect that approach to be fairly easy.

But if I want to create the account and assign the employees in one form, I turn to p. 490 "Multiple Models in a Form". Let's look at the controller and view for edit/update (I might be able to figure out the rest once I have this part).

def edit
  @account = account.find(params[:id])
  @account_employee_relations = @account.employee_account_relations # I think this is an array ?

# I haven't worked on update yet since I can't get edit to work...but I'm sure this won't work.
def update
  @account = account.find(params[:id])
  if @account.update_attributes(params[:account])
    flash[:notice] = 'account was successfully updated.'
    redirect_to :action => 'show', :id => @account
    render :action => 'edit'

I'm quite lost on this section of edit.rhtml:

<% form_for :account, @account, :url => { :action => "update", :id => @account } do |form| %>

<!-- I think I want to loop over all the assigned employees like this: -->
<% @account_employee_relations.each do |r| %>
<!-- Now I need a fields_for...over r ? -->
<% fields_for r do |f| %>
   <th><label for="x">Employee:</label></th>
<!-- I want a selection box listing all the employees, with the currently assigned employee as the default selection -->
   <td><%= f.select(:employee_id, [array of names] %> THIS DOES NOT WORK!
   <label for="x">Role:</label>
   <%= f.select(:role, @account_employee_relation.possible_roles) %></td> <!-- possible_roles is defined in the model -->
<% end %>

Any help is appreciated!