Namaste, I want two attachment in mail compose wizard by default,

I am passing this context.

ctx = dict(
            default_model='purchase.order',
            default_res_id=self.id,
            default_use_template=bool(template),
            default_template_id=template.id,
            default_composition_mode='comment',
        )

currently we can only pass one template in deafult template_id, I want to pass two template. How can I achieve this?