I have to pull up on the latch rather than the backplate to keep the cable in. I get in by digging a slot in the front to keep from skidding - then stepping in.
That's what you should do... and make sure you don't have a bunch of snow under your boot...that will force the cable out of the guides when you tighten it. Another way is to use whatever is around. A tree, a trash can, a bench.... to help you hold your balance and lock in.
2015/16 -3- Kirkwood days
Arbor A-Frame 158 2009-10
Jeremy Jones Hovercraft 156, 2011/12
Subaru WRX 06