Yep, looking like I can't do that.
Here's what my start menu currently looks like:
I don't need or want anything else pinned there particularly. I have taskbar and desktop shortcuts for anything else that's used frequently, and the all apps page (which, while I'm ranting and raving,
also has a bunch of wasted space since it remains at the full width of the start menu when you click into it!) for anything used infrequently. That's a lot of screen real estate being used for five shortcuts, four if I remove the Task Manager one now that I'm training my brain to right-click the start button instead of the taskbar.
Genuinely don't get how that's an improvement on the 10 menu. I'd have 8/8.1's start screen back over this, at least there were third party tools to make custom launcher tiles for it...