How to correctly use readonly=yes with the sqlite driver?

Hi! I want to use a sqlite database in readonly mode, which I found mentionend in the docs 1. Unfortunately no examples were given, so I tried to infer the usage by inspecting core/driver-sqlite.c. If I interpret it correctly, this should have worked:

/etc/dovecot/dovecot-sql.conf.ext: driver = sqlite connect = readonly=yes /var/vmail/virtual.sqlite

user_query = #...

Unfortunately, dovecot tries to open a file named "readonly=yes /var/vmail/virtual.sqlite" instead. I have no idea why the option is not parsed. Is this a bug or am I using the feature incorrectly?

Best regards, oddlama