MarkT:
Ah yes, that's odd, I'd have thought they would choose the on-chip resistors appropriate to allow equal external resistors (chip designers usually think carefully about the parts count on external circuit). So you need the two end resistors to be 3/2 the size of the other 5. Or use 9, make the end ones 1/2 the value of the others, and ignore the first and last taps.Still with 1% resistors 7 equal value ones would actually work I think, on-chip resistors have very good matching.
I think the chip engineers were expecting people to use two resistors per chip (that's why the datasheet uses "R1" and "R2" in the tables). It's what I'd do...