If you have dry snow that won't adhere and it's freezing outside, just pour some water over the snow, then shape it...
what i did: i put a wooden pallet up against the wall, covered it with astroturf and snow, then put snow on the transition, just a pile, then sprinkled water over it, shaped it and voila, it immediately froze and an hour later it was super hard, so i had the perfect wallride....
same could work for regular jumps, just make sure your sidewalls are wide enough and are slanted, if they're straight down they'll crumble under the weight of a skier....
later when the jump is frozen solid you can digg off the sides straight to make it more esthetical....