How to dynamically add properties to a ROAR representer?

I am using ROAR to implement an API for a rails application. This application deals with tickets that can have attributes like a subject and a description, but also have user defined attributes. For simplicity lets assume a ticket looks like:

class Ticket  attr_accessor :subject, :description  def custom_attributes    # in reality these attributes depend on the current ticket instance    # they are not hard-coded into the class    [['priority', 'high'], ['Operating System', 'Ubuntu']]  endend

The desired JSON output for such a ticket looks as follows:

{"subject": "Foo","description": "Bar","customField1": "high","customField2": "Ubuntu"}

Now you might already see the problem. All properties are immediate children of the root object, this means I can't write that up as representer:

class TicketRepresenter  property :subject  property :description  # Need to iterate over instance members on the class level here...end

Is there some mechanic that ROAR offers to accomplish that? E.g. a callback that is executed in the context of an actual instance, e.g.

def call_me_on_write  represented.custom_attributes.each do |attribute|    add_property('customField1', attribute[1])  endend

Is there something like this in ROAR that I have overlooked to accomplish this?

I looked in both the docs for ROAR and the docs for representable, but could not find anything.

Disclaimer

I tried to simplify the actual circumstances to make the question more readable. If you think that important information are missing, please tell me. I will thankfully provide more details.

Out of scope

Please do not discuss whether the chosen JSON format is a good/bad idea, I want to evaluate whether ROAR would support it.