While your home ambient is somewhat low, this is in many ways the beauty of the gradient. If you place you snake your snake in an enclosure with a 90-92 spot and a (let's say) 68 spot, you will simply observe the snake will cling to the warmer parts. I doubt you'll actually end up with an RI.
Additionally, as other posters have pointed out, this is the lowest temperature in the cage (68). In the "middle" area, you probably have somewhere in the 70s, so if the snake wants a middle group temperature, that area exists. If you add a RHP on the cool side with just kraft paper, it is just going to give you a slightly warmer spot on the cool side. Your ambient won't change.
One thing that is often not discussed is the addition of more thermal mass. Do you have any sizable rocks you can add to the enclosure? If you place one under the RHP, it will heat up and likely give off a little extra heat to the environment.
All that said, if you set your hot side to 92 F, what is your cool side temperature? As foo for thought, in Ghana and other parts of Africa, minimum temperatures can range from 66-77 F throughout the year.