You may be able to make an adapter out of thin sheet metal and add spacers. I've seen wine corks and longer bolts used as spacers behind the bottom bracket. Zip ties and Yankee ingenuity might work too. I just use the bigger tires ( 35mm-41mm) and enjoy the added shock absorption. My speeds aren't affected much if any. As you know the Crosscheck is designed for larger than 28mm tires. A triple crank would be my suggestion to get the low you need for climbing when loaded up. A triple as an option for this bike, in stock form, would make sense.

Moral...........you can't make a Ferrari out of a Jeep.