A Mark says: Yes, I use a rear bag or improvised rear support as often as possible when shooting off a bipod.
The one I use most is a TAB rear bag from Sporting Services. The bag has two hand straps stitched to it to help hold it in the hand, shooting with it either vertical or horizontal.
You can make your own using something old filled with grain, but the purpose-made ones are better as they last longer and are less affected by damp conditions.
A rear bag under the butt of the rifle and squeezed with the left hand (for a right-handed shooter) raises or lowers the crosshairs depending on how much pressure is applied or released. By maintaining pressure on your grip while shooting, you will get a rock-steady position and help the rifle recoil straight back increasing accuracy.
When hunting, a beanie hat or jacket can be tucked under the rifle and adapted in the same fashion.
Mark Ripley YouTube star and extreme-range foxer