Step 1:

In a part model, go to User Parameters to add new numeric parameters (ft, mm, etc.).

Select consecutive unit type (ft, mm, etc.).

In Equation, type a model parameter you want shown in a parts list.

Check Key and Export Parameter boxes.

Step 2:

In iProperties create custom properties (ft, in, mm, etc.)

Step 3:

In drawing insert a parts list and edit it to match new iProperties (ft, mm, etc.)

Done!