You can replace the freehub body with an 6,9,10 speed body, but you will need to replace the axle and redish the wheel. You will need to spread the rear triangle because it is most likely 126mm.
It is easier to stick with the 7 or go to a new wheel.
You could go with a half-step with a grandpa gear. Half step gearing would be spaced 20% in the back (11,13,16,19,23,28,34) with something in front spaced 10% like a 22, 40, 44. With an occasional double shift you have 10% spacing on all of your gears except for the very low bail-out grandpa gears.