There are a variety of different jade trees; this includes some with naturally thicker trunks and others which grow thin like vines. So you may be battling against the way the plant grows naturally. Essentially, you may the wrong variety of jade tree for what you are aiming to achieve.
If this is the case, I suggest you begin by looking around and purchasing a variety that has a thick trunk. This will likely solve half your battle. With shaping plants for bonsai you can't force an azalea to look like a pine tree.
Most well watered jade trees are extremely hardy and you can literally hack one to pieces and all the pieces will grow into new trees. The only thing about pruning in spring is that you will get some growth back by the end of the growing season, whereas if you prune in winter you will be left with an ugly plant until summer.
What you do need to do if you want to concentrate the growth towards the center is trim the ends of new growth. If the branch has grown quite long, don't be afraid to cut back aggressively, (depending on the size you are wanting to achieve and the leaf size) maybe an inch back from where you want the leaves to appear. Once you have one branch growing to the right length then just remove any new growth in coming years. The plant will use this saved energy on growing the trunk.
Usually to make a nice looking miniature plant with a thick trunk also consider only having a few branches coming out from the trunk. This will make it look less like the first plant in the question you linked and will have the benefit of more energy going into trunk and branch development.
Also be aware that thick trunked trees don't grow overnight, you need to ensure your plant is well watered, fertilised and has a decent enough sized pot. You don't grow thick trees in small pots, this is a myth. Most bonsai fanatics grow their trees in the ground for 2 - 5 years before potting them. They dig them up and replant them annually or just buy them that way.
Don't worry about collecting every leaf to start a new tree, but if you find friends who like the look of your plant then consider giving some away.