There are some popular LoL sites that allow streaming replays into game client. One of the most popular is op.gg There you just download a .bat file.
This is the code, that is needed to play a LoL replay:
"League of Legends.exe" "8394" "LoLLauncher.exe" "" "spectator spectator.op.gg:8080 5mcWoP1RoN0C1tSSZD3IvxEhGAnIyTYy 1416114864 KR"
Now could anyone familar with POL and LoL can tell me, how to open those specific .exe files via POL?
Since I didn't find any info about it I did it myself. This is what worked for me.
Ubuntu 14.04 / PlayOnLinux 4.2.2
Hope it helps