Actually there is a workaround. You can create a package based the library you want to use and with a little luck it will work fine. It can be a dummy package (i.e. only headers).
Thats true and it is also true that in one point in the past, I was experimenting with "automatic external header package".
Anyway, all of that failed, because system headers are usually extremely full of macros -> results of parsing were nil.
That is why I believe we must deal with macros first, then do external headers.