John McCormack shows two ways to connect to an Availablity Group listener with read-only intent:
SQLCMD
The -Kreadonly switch is your key to success here but remember to also specify the database using -d. When not set (and with an initial catalog of master for my login), I found I always got the primary instance back during my check. This simple omission cost me hours of troubleshooting work, because I was convinced my listener wasn’t working correctly. In fact, I just wasn’t testing it correctly.
There’s some good information in here for sqlcmd and for SQL Server Management Studio.