We currently do not allow you to choose a loction for the index and as you mentioned it is hard coded. We have recieved requests to allow users to choose the index location as well as move an existing index to a new location. As you mention the Service only uses one thread and there is currently no setting to change that behavior. Also, changing the service priority will not speed up the indexing process. I will pass your enhancement requests along to the team.
Craig S. Godfrey Software QA Engineer Autodesk, Inc.