Hi,
had tried several things now and found a way to get it working with an individual Archive folder by editing the LS-GN Prefs file:
I noticed that the file requester at the beginning and the sIBL prefs dialogue don't save an individual path into the prefs file, but writing that path manually solves this issue.
Also noticed that sIBL is the only plugin with a "P" flag in the lock-column in Layouts "Edit Plugins > Layout commands" (don't know what this means, just saw it)
(OB still crashes with this method, but I don't use the default path to the LW Preferences for OB, this might be another problem and I have the feeling that NewTek changed the LScript system on cocoa LW).
A drive component doesn't seem to be necessary on OSX, path starts with /Users/'user-short-name'/'FolderX'/'FolderY'/'FolderZ'/... up to the Archive root.
(But I'll check if it makes any difference to implement a drive component - I just don't know yet how OSX handles the drives internally, as a user can set whatever name he wants to have for a drive, there doesn't seem to be a fixed C:\ name)
(I've given a description on NewTek Forum:
http://www.newtek.com/forums/showpost.php?p=1000759&postcount=14)