Prefaced to say I don't know anything about bernina machines and their walking feet, but every other machine shank and walking foot I've ever seen or used...if you want to do straight line quilting use the L-shaped tool that comes in every box of feet/attachments. The long side pokes into the shank, or into the walking foot body and you can set it any distance from the foot you like from 1/4" to 2-3". Once you set your line with a piece of tape, or the edge of a patch, you use each successive line of stitches to run that dropped down L shape along, making each row equidistant. Those foot attachments go clear back to the 1800's machines and there was one in my newest machine box of bits.
I absolutely love using it for circular or straight line quilting. If Bernina doesn't include one shame on them.