@bwang-tecoustics
I want to acknowledge that you are correct in your assumption that Inventor is not able to import an ISOGEN file.
The best that I can offer you at this time is to post your request on the Inventor Ideas forum:
http://forums.autodesk.com/t5/inventor-ideas/idb-p/v1232/tab/most-recent
Thank you for your Ideas and I am looking forward to seeing on our Inventor Ideas forum.
Bob Holland
Autodesk Product Support