First install GRASS GIS.

# switch to root
su -
 
# replace USERNAME with your non-root username who installed GRASS GIS
if ! echo $PKG_CONFIG_PATH | grep -q /home/USERNAME/usr/local/share/pkgconfig; then
  echo 'export PKG_CONFIG_PATH="USERNAME/usr/local/share/pkgconfig:$PKG_CONFIG_PATH"' > ~/.bash_profile
  . ~/.bash_profile
fi
 
# install qgis; build queuefiles, not packages
sbopkg -k -i qgis