I have raised a similar question at Digikam doesn't see its own symlinks. Reading the manual suggests that digikam (under Export to Local computer) can create symbolic links “to avoid duplicate files”. Yes it does, but the trouble is that digikam seems unable to see those links as “images”, unlike several other viewers such as Adobe Bridge, IrfanView, XnView MP, Krita, Handy Viewer, ImageGlass.
If the feature worked as suggested in the manual, I think it would satisfy your requirement. But it has not worked for me, at least not without having recourse to ImageGlass etc.