Gimp-run makes every version of gimp to a portable version:

The name must be:

gimp-run-"version of gimp".exe, maybe:

gimp-run-2.8.exe

That would start gimp-2.8

The autoit script reads an ini file, but this is not neccessary.
If there is no ini, the program will:

add gimp/bin directory to the system path
set GIMP2_DIRECTORY environment variable to gimp/.gimp-"version of gimp"

and starts gimp/bin/gimp-"version of gimp"

There must be made one change in the gimp/etc/fonts/fonts.conf
There is a line like:

<cachedir>WINDOWS_TEMP_DIR</cachedir>

important is the <cachedir> and </cachedir>

Between these two tags, write what you want, with gimp-run, the 
fontconfig-cache will be created in the directory in gimp/bin

I have

<cachedir>FontCacheDir</cachedir>

so fontconfig.dll will create its cache directory in

gimp/bin/FontCacheDir

Be aware:

Starting gimp the normal way (with gimp-2.8.exe), gimp will
not use the userdir, that gimp-run-2.8.exe uses, but the userdir
in your home directory and the fontconfig-cache will be created 
in the directory you started gimp-2.8.exe from.
