Thicker mash might help. Go down to 1qt/lb grist. Could do separate mashes but that would be kind of a PIA
There is no sin is using some malt extract to get a higher OG. My MT is a 25 galllon SS kettle that allows me to get 20 gallon batches. For something with a really big OG I would rather add some extract to the boil than get a smaller batch.
There are a lot of Barley Wine recipes that call for extract to get that big a beer without larger equipment.