I am trying to create a wizard, launched from a button in res.partner's form view, which has two buttons on its footer (besides the 'cancel' one): the first one launches a method that does stuff inside the related res.partner record (but it's not important to the main problem); the second one opens the email form with precompiled values (again, from the related res.partner's recordset values).

My question is: how do I prevent the wizard from closing when I click on the "Send email" button which opens the email form, so that (after I've finished with email itself) I can go back to the wizard and click the "Execute action" button?

I am using Odoo 8 with Python 2.7.14.

My code:

1- the button that launches the wizard (from res.partner):

    <button string="Execute action" type="action"
        name="%(execute_action_wizard)d"
        attrs="{'invisible': [('action_required', '=', False)]}"
        class="oe_highlight"/>

2- the action that launches the wizard:

    <record id="execute_action_wizard" 
        model="ir.actions.act_window">
        <field name="name">Execute action</field>
        <field name="res_model">
            account.payment.action.wizard</field>
        <field name="view_type">form</field>
        <field name="view_mode">form</field>
        <field name="view_id" 
            ref="execute_action_wizard_form_view"/>
        <field name="target">new</field>
    </record>

3- the buttons within the wizard itself:

    <button name="compute_execute_action"
        string="Execute action"
        class="oe_highlight"
        type="object"/>
    <button name="open_form_send_mail"
        string="Send email"
        class="oe_highlight"
        type="object"
        attrs="{'invisible':[('send_mail', '=', False)]}"/>

4- email form method: 

    @api.multi
    def open_form_send_mail(self):
        self.ensure_one()
        template_id = self.email_template_id.id
        partner_id = self._context['active_ids'][0]
        compose_form_id = self.env.ref(
            'mail.email_compose_message_wizard_form', False).id
        ctx = dict(
            default_res_id=partner_id,
            default_use_template=True,
            default_template_id=template_id or False,
            default_composition_mode='comment',
            default_model='res.partner',
            default_partner_ids=[(6, 0, [partner_id])],
            default_subject=_(u"Client email")
            )
        return {
            'name': _('Compose Email'),
            'context': ctx,
            'type': 'ir.actions.act_window',
            'target': 'new',
            'res_model': 'mail.compose.message',
            'views': [(compose_form_id, 'form')],
            'view_id': compose_form_id,
            'view_mode': 'form',
            'view_type': 'form',
            'flags': {'action_buttons': True},
        }

Please help me out. This is driving me crazy.