All you need do is make the normal force of your butt in your seat be +1, which is completely doable with the right helical trajectory.
Think about it. When the aircraft is inverted, to maintain a perceived +1G in your seat, the aircraft has to be accelerating toward earth at the equivalent of 2G, which is the acceleration of gravity plus the perceived 1G on your butt. That's the equivalent of 64.4 ft / sec^2, or a descent that increases by almost 4,000 ft/min for each second the aircraft is fully inverted.
If you fly a helix that starts in level flight and sees a perceived constant +1G in your seat, you will end up in a steep dive that will require much more than 1G to recover from. Both Hoover and Johnston executed their rolls by first pulling up into a climb (>+1G) to reduce the altitude loss when making the maneuver, but both saw greater than 1G at the beginning of the loop, and likely at the end. It's simple physics.