yes in /website_form  One2many return a list of ids. so if you archive this type of functionality then you want to override extract_data().

like, 

def extract_data(self, model, **kwargs):
    product_ids = kwargs.pop('product_id[]', '').split(',')
    quantity = kwargs.pop('quantity[]', '').split(',')
    model_record = request.env['ir.model'].search([('model', '=', 'product.line')])
    product_line_ids = []
    line = {}
    for index, product in enumerate(product_ids):
        line = {
            'product_id': product,
            'quantity': quantity[index]
        }
        product_line_ids.append((0, 0, line))
    data = super(Website, self).extract_data(model, * * kwargs)
    if data['record']:
        data['record']['product_ids'] = product_line_ids
    return data

Suppose you have a multiple line on form view for product, add this list in form, for ex.

<input type="text" name="product_id[]"/>

try this it will help you. Thanks ;)