That is not possible right now (FME 2016.1) but I've solved it with a Directory & File Pathname Reader reading all dwg-files and then a StringConcatenator:
" "C:\Program Files\Autodesk\AutoCAD 2016\acad.exe" "@Value(path_windows)" /b "c:\script.scr" "
And then send the string to a SystemCaller transformer.
The script.scr is a AutoCAD script-file that just calls a AutoCAD lisp-file inside AutoCAD and then closes the DWG-file.
The lisp-file gets the list of Paper Spaces in the DWG-file and stores it is a txt-file with the same file name as the DWG-file and in the same folder.The lisp file could look something like this:
(defun c:layoutToFile() (setq fl (open (strcat (getvar "dwgprefix") (getvar "dwgname") ".txt" ) "w")) (write-line (vl-prin1-to-string (layoutlist)) fl) (close fl) )
Then you can use the txt-files to read the Paper Spaces with a FeatureReader or with linked workspaces with the WorkspaceRunenr if you have published the parameter "Read Selected Paper Spaces".
Perhaps not that straight forward but it solves the problem.