Menu path: Sessions > Chromium Browser > Chromium Browser Global > Custom Setup > Custom Command-Line Options

Here, you can define command-line parameters that are passed to Chromium on startup. The syntax is exactly the same as if Chromium would be started from a terminal. 

Custom command-line parameters: One or more command-line parameters. Multiple parameters are separated by whitespace.

Example:

--proxy-server="socks://localhost:8080" --incognito