Custom Checkout Fields for MarketPress


I have read on the forums about adding custom fields to marketpress checkout form, I have also asked and got reply by email that I should try CustomPress plugin. I have it installed and I am able to add fields but I see that these custom fields are shown on the post editor as additional attributes, but I want them to be input fields on the checkout page to collect more data in addition to the Shipping and Billing fields, there is more than 10 fields to be added in addition to the Billing and Shipping fields.

1. How to add the custom fields to the checkout form and make them as input fields so that customers can fill in the required data?

I know about the "Additional Notes" textbox, I need to expand the form with additional fields.

2. How to embed those input fields to the checkout form without editing code? Will the shortcode be able to modify the checkout form and include the custom fields on submission?

I need this for currently 46 sites using the same theme and so modifying the template files will not be a good idea because each site admin will possibly have different fields.

Thanks for your help in advance.