server-tools/cron_run_manually/view/ir_cron.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>

        <record id="ir_cron_view" model="ir.ui.view">
            <field name="model">ir.cron</field>
            <field name="inherit_id" ref="base.ir_cron_view" />
            <field name="arch" type="xml">
                <field name="args" position="after">
                    <button name="run_manually"
                            string="Run now"
                            type="object"
                            />
                </field>
            </field>
        </record>

    </data>
</openerp>