I don't really like just telling you how but since you're at least trying I will in this case.
Everything up to step 5 is right but instead of putting another coin ontop of the ones on the ground, you can just put the z shelf right ontop of the bottom coin. That's because when you take it, the z shelf, out onto the rollers, when it rolls back in it goes ontop of the bottom coin - making the slightly higher coin pointless. That's not why you're having problems though, just a little extra tip.
Step 6, as you correctly pointed out, is where you're going wrong. Just like in the guide, pull out the z shelves (or whatever 'table' item you're using) and put them on the rollers. While they roll towards the stack, merge a chair into them and let them roll in. That step is the part which will let you place anything into the stack you want.
You should try to understand that when I say it let's you put anything in the stack, I should also say (Verrou got this from my 'clue' earlier) that it also let's you put anything anywhere in the stack. Sorry to be cryptic but you need to understand how it works for yourself.








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