How to do polymorphic associations in Doctrine 1.2?

Question

Is it possible to do polymorphic associations with doctrine 1.2 (!) in symfony 1.4?

I have, for example, the following in my schema.yml:

alBillingElement:
  actAs:
    Timestampable:

  columns:
     id: {type: integer(11), primary: true, autoincrement: true}
     object_type: {type: varchar(20)}
     object_id: {type: integer(11)}
     task: {type: varchar(20)}
     parameter: {type: text}
     amount: {type: float}

object_type contains the model name of the object referenced by object_id. Can I somehow define a relationship so that i can query the "object" using relations?