Thanks for your feedback on the gem, great to hear that people are finding useful!
Unfortunately Salesforce does not offer any (public) API for executing reports. Your only officially supported option is to run SOQL queries to get the data that you need and then build the presentation yourself.
That said, there must be some kind of private API for it, because you can use the Salesforce Connect for Office plugin to download reports into Excel spreadsheets and keep them updated there:
I would LOVE to see someone reverse-engineer that feature and figure out how to pull the report data out programatically. If I had a wealth of time on my hands I would do it, but alas I don't. Please let us know if you figure it out! :-)