We're working on this, but the GoBack feature was initially intended to be an option to allow subjects to return to the immediately preceding item--a useful thing when using scale responses given their automatic procession, but no so much so when designing a test like you're describing. In the next version, I expect we will implement a feature like you are describing--a way to let them go through the questions.. and then go through them once again, automatically skipping ones they have already answered.. Kind of like a "come back to this one later" option. I'll cc this to the suggestions area.

-Blair