Two CAD unit systems in one PDMLink

As we are facing the challenge of having CAD data with different unit systems (US and SI) in PDMLink, I am looking for a solution to be able to indetinfy the origin unit system on the drawings. The information is stored in the 3D model of cause, but there seems to be no way to bring this information to a parameter, which can be shown on the drawing. Any suggestions except defining the value of such a parameter manually?