Did you guys found any solution? I'm facing exactly the same problem.

There is potentially a module for this as this is a very much desired request. https://github.com/odoo/odoo/issues/4231

If I don't find it satisfactory, then I will start developing my own. Also check Odoo 9 and see if this is maybe something that is being worked on, as that code should easily be ported.. It only needs a slight change to the API code, to allow another parameter, that defines to add a payment or not.

I have so far added the button on the POS Screen. Any idea how I can post the current order object to server without firing the payment procedure? The problem with invoicing is that it marks the order as paid even before payment is received against the invoice. Also, many bar customers are walk in customers, meaning that the business may not have their records.

(sorry I cannot use the comments on my own question because I dont have enough points. Please upvote my question)

Without modifying the system, I would use the Customer Invoicing option which raises an invoice first and take a payment later. It is possible to create a user who only is allowed to do invoicing and payments