" Variable resistor in 10PPM tempco are going to cost too much."
(all below IMPE, )
not exactly.. you do trimming of existed value to a very small amount, a fraction of ohms, so let say adding a resistor in a sequence , 10ohm 5ppm + 100 (200 -500) ohm trimpot at 100 (200-300) ppm ... you may calculate influence by trim-pot, it will be pretty small ...
option2: you may adjust offset of Lt1001, as it in range of microvolts, it doesnt affect opamp TC much. Yet, it not a recommended , but in a millivolt range.
fancy thing: opamp divider to get 10V, TC does influence on each shoulder differently , so if you have resistors with positive and negative TC yo may compensate it place a specific resistor in a specific shoulder. you can do a super fine tuning, a resistor made from a long copper wire, as copper has very high positive TC.