Boysenberries (cross between raspberry and blackberry) are vigorous growers. However, once they finish fruiting, they need to be cut almost to the ground so that the new shoots will give you fruiting spurs for next year. So this doesn't quite solve your problem.
But, the vines do need trellises to climb so the heavy vines don't sit on the ground and the berries rot, which they'll quickly do. If you could somehow make a freestanding trellis close to the neighbour's ugly garage, you'll be okay.
The vines are very heavy feeders and need masses of aged manure and compost, good drainage and frequent watering if you expect good crops. Because of this heavy feeding, they can't tolerate close competition with one another and need about 4 ft spacing between each other. So it looks like you'll need 2-3 plants to cover your eyesore.
Also know that boysenberries may appear ripe but won't be. You'll need to taste them for that very short time they're ripe before they drop. And yes, berries can be frozen in covered poly tubs, in single layers.
When they finish fruiting in about May/June, cut down the vines to almost ground level and keep watering, and renew the manure and compost each year and you'll be swamped in berries next year.
