This is a very confusing scenario. Given that there is no requirement for or expectation of abstinence then an EtG test serves no function whatsoever.
EtG cannot quantitatively assess consumption. Positive could result from dose of cough syrup, mouth wash or fifth of scotch. The test cannot be used as a means of determining impairment or as a basis for back-extrapolating amount of consumption.
I have no idea how your employer will interpret the results but can assure you it is an improper method for accomplishing the purpose you describe.