The Checkout form is no more than a normal HTML form.  However, this time you need to do the whole form without BEE's assistance, as it is not required.

All you need to do is to create a form that submit to /sendorder.htm, like <FORM action=./sendorder.htm>.  The "sendorder.htm" application will pick up the shopping cart and anything on the checkout form, convert it to plan text format and send it as an email to the owner's designated email address (settable from Settings on the blue bar).

One restriction though, if you are using the POST method, you must submit to a real page.  For example, <FORM action=./sendorder.htm method=POST> will not work because sendorder.htm is a Virtual Page application.

There is a way to work around this:

<FORM action="{{PortalObjectName}%SiteURL}" method=POST>
<INPUT type=hidden name=submitredirectto value=/sendorder.htm>
...

Since the site URL is a physical page (the Virtual Page "mother"), the POST will work, and the Portal Object interprets the "submitredirectto" form parameter and redirect the form to the corresponding application.

The above workaround is required only for method=POST.  For method=GET (the default), there is no need of any workaround; the Virtual Page mechanism works beautifully with GET.