For my (freshly downloaded, 24 Mar 2020) Origin version, the WSGF hack did not work.
However, I found https*//chomikuj*pl/Jedrz/Prywatne/Gry/Mody+i+dodatki/The+Saboteur/FOV+Hack+for+The+Saboteur+v1.0 which looks fishy enough but actually did the job. I copied the exe into the game directory (Origin Games\The Saboteur) and started it after starting the game. It's a small window with just one slider for FOV and also has Num+ and Num- work as hotkeys.
On a sidenote, does someone know how to find out my game version? This page says "Origin is already patched to 1.03", but my exe's details say 1.0.0.1.