I don't think you're going to like my answer (and it may not be true).
But because of the Turbotax issue (which I also encountered), my conclusion was that there is no way to file as jointly married through Turbotax AND file a W-7 at the same time. Yes, you could use 999-99-9999 as the social, but it's supposed to be left blank for the ITIN application.
And, annoyingly, Turbotax will not let you file jointly married without a SS# entered.
What I wound up doing was going through H&R Block, specifically to someone certified as an IRS "acceptance agent" for the purposes of filing a W-7 and a return. Yes, I had to pay about $300 for the filing fee, but the benefit is that you don't have to send in any of your spouses documents (license, passport, etc.). They just make copies of it at the H&R Block office.
You'd have to call H&R Block to find which one has someone who is an IRS "acceptance agent". That's what I did and there was only one office who employed someone with that certification.