builders.rb

class MyBuilder < Merb::Helpers::Form::Builder::Base
  
  def my_awesome_method
    
  end
  
end

class AnotherBuilder < Merb::Helpers::Form::Builder::Base
  
  def another_method
    
  end
  
end

# --- To get it to work, I have to define the following helpers ---

def my_awesome_method
  current_form_context.my_awesome_method
end

def another_method
  current_form_context.another_method
end

view.html.erb

<%= form_for :something, :builder => MyBuilder do %>
  <%= my_awesome_method %>
<% end =%>

<%= form_for :another, :builder => AnotherBuilder do %>
  <%= another_method %>
<% end =%>