I need to create a type of one2one between several models, does someone have a clue how to manage this? Here are the facts:

• I have the default model crm.lead
• Now i need to add more two models e.g.
• • crm.lead.foo and crm.lead.bar
  • Both new models are linked to the crm.lead object using a field lead_id as many2one
  • lead_id = fields.Many2one('crm.lead', string='Lead', ondelete='cascade')
• Now in the crm.lead i need to add the relation by sth like a "one2one" that doesn't exist.
• I think the best/better way is to add the relation with a Many2one field from the crm.lead to link it to the foo and bar (writing the value on create)
• • crm_lead_foo = fields.Many2one('crm.lead.foo')
• Basically the link works and i can choose the foo/bar and edit it's fields
• But the edit does only work when opening the foo/bar in a new form
• I need to show the form of the crm.lead.foo form inline in the crm.lead form, is there any widget that can manage this?

Note:
I know, I would be able to add all needed fields as related fields into the crm.lead form to make them working inline. But I need to add several new models (not only 2) with many fields each. Additionally i will need to add the models based on the opportunity_id also in the sale.order and the project.project forms.... so i'm looking for a clean solution without adding much trash to my core models.

Thank you for your help and ideas!