The plugin you found doesn't have a 1:1 ratio between Heroku instance with build jobs since it takes the job name as parameter, so you should be able to run any number of jobs from a single Heroku instance.
As for passing a space in a job parameter, it depends on how the arguments are split by this line, I don't know enough ruby to make sure that it would avoid breaking quotesword split is made on spaces so quoting won't change anything. Another wayYou could possibly try to use the HTML spacing character %20
and see if it works.?
Personally I would try to use the plugin to run the correct job with the associated parameters directly instead of going through filtering jobs.