[aur-general] Define variable for psimedia

I want to add PKGBUILD psimedia in AUR, but to work is required to define a variable PSI_MEDIA_PLUGIN. How best to do this? I can just write about the need to define a variable in ~ /.bashrc or to include in the PKGBUILD the line: echo 'PSI_MEDIA_PLUGIN=/usr/lib/psi/libgstprovider.so' >> /etc/environment