Hi, It's I wile ago I've been there, and if I recall correctly, they don't have a plus-size luggage desk in Geneva/Geneva airport, but they do have lockers. Dependent on their size, your ski's might just fit (but I really don't know...)
This is the (German) Gepäck/luggage site from the station in downtown Geneva. They have phone number that might help you out with locker-size, storage possibilities and prices on one or both of the stations (downtown/airport).
is the sbb's forum where you could ask for help if the call doesn't work out.
I'm curious what solution is best in the end (as I might end up with the same challenge in the future 😃 ).
Good luck and a better winter 😉