I Know a quick and cheerful method for you. set the units of your part to meters and then when you create your drawing your mass property info will appear as Meters and Kgs, then insert your dimensions, (again these will be shown in Meters) window select them all and do a right hand mouse buttton to activate their props, in there you can choose to select the individual units, ie mm.
There is possibly another method by draging a design table into your part, (you don't need to create a family of parts) just one, and you can link custom props in there and use the power of excel to tweak the units to the values you need.
hope this helps.