Use the 3DForcer transformer to add the value of your attribute as the Z value.

Thank you! Really simple. I expected extracting an attribute from a GIS dataset into the z-value of a CAD file/level to be a not uncommon activity, so was surprised I couldn't find anything about it in the public forums, so thank you. (my delayed acknowledgement has been caused by wild weather activity in southeast Australia, and the loss of power, telecommunications, etc.)