In reply to pec: yes a heel lift or specialist orthotic insole would allow you to fit into the boot, but you would find that a soft ski boot would cause you to experience metatarsalgia, pain under the bases of the toes and diastasis (widening) of the sub-talar joints on forward lean in a soft boot , or loose top clips, a specialist boot fitter will ensure that the relationship between the angle of the tibia and the sole of the boot is correct and comfortable, otherwise damage to the mid foot will occur.
Good luck.