There are 3 methods I use:
1. Lean it over on the sidestand far enough until I can push something underneath then level it up and 'wriggle' into the middle of the crate or whatever.
2. Put it in 1st with a box to the side (or a helper to push box under) then stand it upright and lift by the front wheel using the rear as a pivot, then move to the side, onto the box.
3. Similar to above but use a strap to hold the front brake on and lift from the rear.
None of the methods are ideal and you need to use a good lifting technique to avoid back injury, but they work for me.