[tex-live] Can a definition in user-space "texmf.cnf" reference the same definition in system space ?

[Philip Taylor]

In order to allow a Dropbox-based TeX suite to find the images it
requires on different systems with different Dropbox locations, I have
manually tweaked user-space "texmf.cnf" to re-define TEXINPUTS.xetex to
include a sub-directory of my Dropbox folder.  However, in order to
avoid diagnostics from the run-time system I have had to manually copy
the value from system-space "texmf.cnf" into my user-space variant.

What I would /like/ to do is simply reference the system-space
definition, but the following :

	 TEXINPUTS.xetex =
$TEXINPUTS.xetex;D:\Users\Chaa006\AppData\Local\Dropbox\LPL\Catalogue\Images\Complete\PDF\Embedded

leads to the following diagnostic from the run-time system :

	warning: kpathsea: variable `TEXINPUTS' references itself (eventually).

and to overcome this I have to modify the above to :

	TEXINPUTS.xetex =
.;$TEXMF/tex/{plain,generic,}//;D:\Users\Chaa006\AppData\Local\Dropbox\LPL\Catalogue\Images\Complete\PDF\Embedded

Is there any supported way of referencing the system-space value of the
name as opposed to simply copying the value and appending ?

Philip Taylor