Also just using off-the-shelf LC single mode fiber cables has worked well for me.
Discussion
well, i found a way to turn off the wifi on this blasted thing anyway, so now i have a spare router with SFP port on it.
i have the fix handy for reversing the disabling of it, i must remember to keep it around so i can reverse it before i hand over the keys when i exit this rental.
for future anyway i now have a neat little router that i can use on gigabit ethernet or if it's got fiber i can get an SFP unit for it, if there isn't a way around disabling the wifi on a later occasion. i kinda wish i had found the solution before i slapped down i forget how much, 60 euros or something. still, could be worse.