I guess the obvious answer would be to bench with an arch, and keep trying to arch more every time.
I did notice that my back was aching when I first started to arch a lot (relatively), but that subsided once I did it for a few weeks, and I probably shouldn't have started doing it on my heavy bench days.
I've recently been noticing that the arch has helped a lot with my bench, and not only due to the shorter distance. I really feel like I'm able to use my legs better and get more weight when I arch correctly.
I notice it a lot when I do my dynamic effort benches with approx. 60-65% of my 1RM. If I'm not in the groove, or not arching as well as I should, the bar will go up quickly, but no wheres near as fast as when I'm arched correctly.
The bar seems to fly up as if my back is a spring-board that's taking the energy from my legs and sending right into the bar. The bar goes up much faster and feels almost weightless.
My arch got better just from doing it more often (every time I bench), but I'm sure there are other ways too.