Hello @bmichael!
Totally understand your use case for wanting to use a Service account. I was looking around the forms and found this post related to both setting up the connection to Google Service Accounts and using JWTs to avoid errors for this process.
Justin at the top responds with some resources related to JWTs and a couple comments down, Joe shared an app which demos the setup but just needs you to fill in the fields he specified.
Let me know if this helps!