Only set target and minimum value or maximum value for characteristic in Inspection Plan ?

Hello

In our customer rollout implementation, we noticed that for some countries, some numeric characteristics are set in the inspection plan with only a minimum or maximum value. 

For example, when measuring a density, sometimes they only need it to be under or over a given measure. 

Now, in Quality Management, I cannot enter either a min value or a max value, even if those fields are not defined as mandatory.

How could we do to do so? Note that the target value is not an issue here, we don't mind entering a value for it.

If we were to enter a very low value for min or a very high value for max depending on the case, that would not be convenient as the results are then used for generating a report.