More info than you ever wanted to know on environment variables. Not completely sure if up to date, but give it a shot, I would suggest adding the
export LV2_PATH=.... line to your ~/.profile file and see if that works for you. Some graphical environments don’t always process .bash_profile as they don’t always launch a bash shell, so hopefully this will get it in your graphical environment as well. Haven’t had a need to test it, but give it a shot and see what happens.