Too be honest i’m not sure. Spend some time to confirm what you/they say but it might work if Sx is the same as L (measure between Sx & N). Internet seems to say its the same as input (230v) but i don’t have a unit close so i can’t check personally. If its indeed the same as L then in theorie you could feed your switch with L instead of sx and go to S1/S2, if there is no “smart” thing going on inbetween Sx/S1,2.
However, not a single fibaro wiring diagram supposes that solution. It might just work fine but i’m not sure what it will do on “millage” and besides that, i mostly like to follow the official diagrams when i’m wiring the place where i also sleep.
I am curious though, so let me know if you find anything on that. Mayby someone else can chip in on this.