Add the following code snippet and file to your site specific plugin. Adds a first step to the progress display at the top of the Event Espresso Single Page checkout. The step is skipped.

an_example.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_action(
    'AHEE__EE_System__load_espresso_addons__complete',
    'my_add_extra_step_class_autoloader'
);
function my_add_extra_step_class_autoloader() {
     EEH_Autoloader::instance()->register_autoloader(
        array(
            'EE_SPCO_Reg_Step_Add_Extra_Step' => 
            plugin_dir_path( __FILE__ ) . 'EE_SPCO_Reg_Step_Add_Extra_Step.class.php'
        )
    );
}

add_filter( 'AHEE__SPCO__load_reg_steps__reg_steps_to_load', 'ee_add_extra_reg_step' );
function ee_add_extra_reg_step($reg_steps)
{
    array_unshift(
        $reg_steps,
        array(
            'file_path'  => plugin_dir_path( __FILE__ ),
            'class_name' => 'EE_SPCO_Reg_Step_Add_Extra_Step',
            'slug'       => 'select_tickets',
            'has_hooks'  => false,
        )
    );
    return $reg_steps;
}

EE_SPCO_Reg_Step_Add_Extra_Step.class.php

<?php
class EE_SPCO_Reg_Step_Add_Extra_Step extends EE_SPCO_Reg_Step
{

    /**
     * constructor
     *
     * @param EE_Checkout $checkout
     */
    public function __construct(EE_Checkout $checkout)
    {
        $this->_slug = 'select_tickets';
        $this->_name = 'Register';
        $this->_template = '';
        $this->checkout = $checkout;
        $this->_reset_success_message();
    }

    public function translate_js_strings()
    {
    }

    public function enqueue_styles_and_scripts()
    {
    }

    /**
     * Initialize the reg step
     *
     * @return boolean
     */
    public function initialize_reg_step()
    {
        $this->checkout->skip_reg_step($this->_slug);
        return false;
    }

    public function generate_reg_form()
    {
    }

    public function process_reg_step()
    {
        $this->set_completed();
        return true;
    }

    public function update_reg_step()
    {
    }
}