I don't think you can, without creating links (which will add clutter to what you see in Explorer, as you say).
(You could use normal shortcuts, since Explorer won't show those in its tree view, but they'll still clutter up the file display within Explorer.)
The difference is because Opus's file display is showing the real folder contents of C:\Users<username> while Explorer is showing the shell's "view" of the virtual folder which is tied to C:\Users<username>.
(The tree in both Opus and Explorer shows the shell view of things.)