AutoCAD Visual LISP / AutoLISP :: Append Directories To SFSP With Raster Design Loaded

I am in the process of creating 2 lisp routines, one that loads Support file search paths on the network and one that adds support file search path locally. Each routine will be run depending on the ability of ACAD to find a file on the server. I noticed that when I add the new directories the default AutoCAD folders get replaced. I researched this and found that using the SETENV and ACAD I can include the default support paths. 

The issue I am running into is that not all default folders are being added to AutoCAD when I used the ACAD variable. A plugin folder under Program Data is listed in the original install, but it is not listed when I add my directories and used the ACAD variable to add the default directories. The same thing happens when raster design is installed. The help folder and the install directory for raster are not carried over when using the ACAD variable. 

I am attaching the coding for the lisp routine adding server paths. Is there some syntax I can add to tell it to append to the list instead of replacing the SFSP list?

(vl-load-com)
(setq files (vla-get-files
(vla-get-preferences (vlax-get-acad-object))
)
)
(setq SERVNM (getenv "servername"))
(setq SLSERV (STRCAT "\\" SERVNM))
[code].........