In a bit of a pickle...advice please!

So, I'm dumb and bought a 23 liter carboy thinking it was 5 gallons. Racked into it recently as a secondary because I'm racking onto an oak dowel (will later be used for a 3 gallon carboy as part of a stopper for a lambic. Just "seasoning" it ) and aging it for a couple more weeks than I'm comfortable with doing in a plastic bucket primary. Whoops, there's a lot of head space.

With my equipment, I believe I have three options:

1) Do nothing and hope that off-gassing will create enough co2 to fill the space. It will only be there for 2 weeks most likely. (Probably not a great option)

2) Brew around a gallon more of the same gravity with pilsen DME and hop it to the same IBU's (The recipe is mostly pilsener malt with some spelt).Rack into the carboy and let it do its thing.

3) Rack again into a 3 gallon carboy I have and bottle the rest now.

Any advice is most welcome! Pic below to help in decision making

only two weeks, leave it alone.

I would toss in a tiny amount of some sort of sugar just to get the yeast moving enough to give you a co2 blanket without effecting flavor. you could use dme, corn sugar, honey, whatever really. I've heard of some sour beer brewers doing this to make sure their hard work didn't get too much oxygen exposure and turn to vinegar.

Cool, I appreciate the responses so far. I'm still thinking more along jester's lines just to give the yeast something to munch on and produce some co2. I would just really hate for oxidation to spoil this beer because it's smelling and tasting great so far. Perhaps I'll do some pilsen DME and turbinado sugar...because I love turbinado

amandabab, have you left that much headspace on something in secondary for two weeks before? If not no biggy, I appreciate the opinion anyhow.

Don't touch it. It will be fine

yes. the co2 doesn't need to fill the headspace, just form a thin blanket. outgassing can do that.

I wouldn't leave that much space for a long time though.