Hello.
I am facing the same problems with publishing iAssemblyes to CC.As I know publishing iAssemblyes or any assemblyes to CC is not possible.
Your solution will work, but it has a big minus. If you have a read-only library then you always will have parts in your assembly outside the project folder. I don't like this. I don't think this is a profesional solution. But it can work.
What I like about CC parts is that they are saved in you project folder. You don't have any problems.
What I am going to do is redraw the assembly as a multi body iPart and Publish it to the CC. Offcourse you will only have one entity in your BOM. So that can be a problem.
First of all I want to figure out why Autodesk won't include publishing of assemblyes to CC. It would be so usefull!!!