Backing up an SQLite3 database on embed

I am currently working on a C project that contains an SQLite3 database with WAL enabled. We have an HTTP web interface over which you shall be able to get an online backup of the database. Currently, the database file is reachable over HTTP, which is bad in many ways. My task now is to implement a new backup algorithm.

There is the SQLite-Online-Backup API which seems to be pretty nice. There, you open two database connections and copy one database to the other. Anyway, in my setup, I can't be sure that there is enough space to copy the entire database, since we may have a lot of statistics and multimedia files in it. For me, the best solution would be to open a SQLite connection that is directly connected to stdout, so that I could backup the database through CGI.

Anyway, I didn't find a way in the SQLite3 API to open a database connection on special files like stdout. What would be best practice to backup the database? How do you perform online backups of your SQLite3 databases?

Thanks in advance!