Are you willing to take over maintenance of the package and manage it on an
ongoing basis going forward?
If so:
The ideal process would probably be to get it into Debian so that Ubuntu can
grab it so that Trisquel can grab it.
An alternative would be to work on making a Helper. See
http://trisquel.info/en/wiki/package-helpers
An example package helper that pulls in a package from outside Ubuntu would
be this one:
http://devel.trisquel.info/gitweb/?p=package-helpers.git;a=blob;f=helpers/make-handbrake;h=6ce9ba0148a51b584a8f16cbd9ca59ce78dae31b;hb=refs/heads/toutatis
Notice the EXTERNAL= line. So you'd need to set up a repository somewhere for
the Helper to pull from.
