Don't think you will have any luck getting in from past posts on this matter and I wouldn't personally try as you are likely to be turned away and that is not the way to start a trip or impress your better half!

So options are:

geo772 is offering a single guesting place to GF if you arrive before 16:30, you could always be the gent and let her get guested in for some champers and a quick look around to see what is coming?

Also, consider posting a request in the thread, you never know if someone can guest you both in to GF or CCR that doesn't post on the lounge guesting thread regularly but happens to be there today.

You could simply buy a nice bottle at duty free and bring it in and ask the staff in GC to provide a bucket and ice and then enjoy that as a way to kick off the trip and the soon to be enjoyed status. I've done this in the past and found it a working solution.

To be honest, I imagine the champers in GC and GF are the same, they likely are using the Tat Prelude (hopefully) over the Castelnau...so champers wouldn't be any different, just access would be easier as self serve instead of having to ask.

Hope the trip goes well, congrats on reaching Gold, you sound like you deserve it and will enjoy it in future!