configure problem with xfce-3.8.18

[wolfgang]

in my unusual environment at work i tried to compile and install xfce-3.8.18 
today.

/usr/local is read-only there (it's a common network mount for all linux 
workstations - a writeable local dir is /usr/sue
so i used:

./configure --prefix=/usr/sue --sysconfdir=/usr/sue/share/xfce/etc 
--exec-prefix=$PREFIX --enable-old-style --enable-taskbar 

but during the configure process it kept saying:
XFCE_DIR set to /usr/local/share/xfce
which is read-only, so "make install" exits with an error
i also tried:
export XFCE_DIR=/usr/sue/share/xfce && ./configure --prefix=/usr/sue 
--sysconfdir=/usr/sue/share/xfce/etc --exec-prefix=$PREFIX --enable-old-style 
--enable-taskbar 
same result

editing xfce-3.8.18/Makefile (which kept containing the unwanted path to 
/usr/local/share/xfce) didnt change it either, neither did:

./configure --prefix=/usr/sue --sysconfdir=/usr/sue/share/xfce/etc 
--exec-prefix=$PREFIX --enable-old-style --enable-taskbar 
XFCE_DIR=/usr/sue/share/xfce
(all on one line)

so how can i make it _not_ use /usr/local at all?

regards,
wolfgang