I asked about this elsewhere and was told:
...we didn't implement support for it because it's complicated and there have been very few requests for it.
So that's that, you can't create this kind of bookmark because it's not implemented. I also filed a bug with Apple but the response just quoted the docs at me (i.e. telling me stuff I already knew and had mentioned in my report) before closing it. So, as of now and probably for the foreseeable future, this is not possible.