Actually, there is a simpler way which doesn't require you to modify bootbox code.

The string you pass at the bootbox creation doesn't have to be only text: it can also be html code. That means you can include pretty much everything in the box.

To put a custom form in a bootbox, you can then create it as follow :

bootbox.confirm(<form id='infos' action=''>

    First name:<input type='text' name='first_name' /><br/>

    Last name:<input type='text' name='last_name' />

    </form>, function(result) {

        if(result)

            $('#infos').submit();

});