This is a recent issue for me too, after maybe 50 brews (12 from grain, half a dozen extracts, the rest kits...) having had my first properly 'stuck brew'. I just repitched a 1.079 quad that had stuck at 1.016. That's 80%AA so often would not be considered stuck, but with 15% sugar and a 64C mash (sticking to our British Isles units there!) it should be lower. No rousing or temperature raise to 24C had done the job for me.
You have more unknowns there with the extract, so a forced ferment test would be good, to see if there's any point in throwing in another starter. I saw Dogfish do one on Brewmasters before [SPOILER ALERT] having to chuck a whole batch of their 120. Assuming you've got 23L, a pint sounds too small to me. My 1L active starter with 1 sachet of US-05 (rehydrated first) has bought me 2 extra points in 2 days, with a new small kraeusen on the beer. I didn't go beyond that for fear of changing the taste too much, but it seems to be enough to have shifted things a bit, still going...
It may well be done though, and the only option I can see would be to brew a drier batch and blend it.