> Providing a separate %.d rule would fix this issue

Yes. The following is an example of how to handle C header dependencies. It could be adapted to build css from less and would be an improvement on the blog post technique.

    sources := $(wildcard *.c)

    -include $(subst .c,.d,$(sources))

    %.d: %.c
        $(CC) -M $(CPPFLAGS) $< > $@.$$$$; \
        sed 's,\($*\)\.o[ :]*,\ 1.o $@ : ,g' < $@.$$$$ > $@; \
        rm -f $@.$$$$

It uses the fact that if you include a file which doesn't exist but for which there is a rule to build it, GNU make will build it for you.