OK, portage is amazing. I get it to make a wrapper script for IanniX.
The ebuild is here: iannix-9999.ebuild For instruction on how to install it or the overlay: Pro-Audio Gentoo Overlay
The wrapper is “/usr/bin/iannix”:
#!/bin/sh
cd "/usr/share/iannix"
if [ -n "/usr/share/iannix,/usr/share/iannix/pixmaps" ] ; then
if [ "${LD_LIBRARY_PATH+set}" = "set" ] ; then
export LD_LIBRARY_PATH="${LD_LIBRARY_PATH}:/usr/share/iannix,/usr/share/iannix/pixmaps"
else
export LD_LIBRARY_PATH="/usr/share/iannix,/usr/share/iannix/pixmaps"
fi
fi
exec /usr/bin/IanniX "$@"