Best way to dry out a beer thats already in the keg?

I made a St Bernardus ABT 12 clone, following the recipe in the 250 Clones mag.

I let it sit for about 4 months, so I just figured it was done, I kegged it without taking a gravity reading (dumb I know).

However, I think the yeast I got was too old, and the beer ended up way too sweet.

Is there anything I can do now to dry it out?

I was thing about racking it from the keg (it is already very carbonated, will that even work?) back to a carboy. Letting it warm up, letting all the Co2 evaporate out, and then adding some beano? Maybe adding pitching some new yeast from a big starter at high krausen? Which yeast should I pitch? Any other ideas?

I brewed this beer back in December, so I kinda want to save it. But right now every pint i pour goes down the drain.

I spose I could brew another batch to blend it with, but it is REALLY sweet, not even sure if that would work...

Thanks for ideas.

I haven't done it yet, but if your up for some funkiness, you could pitch Brett and let it sit for a bit. I think you'd need to periodically purge the air or rig an airlock.

How long has it been connected to the line pressure? Why don't you just warm up the keg and then add yeast? You can always just burp it a couple times per day if it is already high pressure.