One idea is to take a white t-shirt and paint on it, saying that you need a ride from Hirtshals and south. And then wear it all the time during the ferry ride and make sure to mingle a lot :) A friend of mine did this one, so i cant take credit for the idea but its quite effective!
Sounds like it might work! Cheers!
Good luck with this. You can try asking around on the boat. When I took the boat to Iceland this summer, I asked a few people for a ride to Reykjavík and of course it did not work. But then I just left the boat as soon as it arrived and waited outside the terminal and got a ride pretty quickly. It is not a guarantee, but I still think you stand some chance. Just as a last resort.
Anyway, I hope you had a great time in Tórshavn and you are now fluent in Faroese:)