I apologize, I misunderstood your question. You should be able to use the --scale parameter as mentioned in the Model Optimizer documentation.
--scale SCALE, -s SCALE All input values coming from original network inputs will be divided by this value. When a list of inputs is overridden by the --input parameter, this scale is not applied for any input that does not match with the original input of the model.
Please let me know if this is what you are looking for.