I did this for a while myself, for the same reasons. Honestly, I wouldn't recommend it. Never ridden the Spyder before, but I used a Kashimax. Short errands and such weren't a problem, but anything over 5 miles had my ass seriously hurting. I won't even ride that saddle now unless I absolutely have to.
IMO, get something with a bit of padding and a vinyl cover that won't absorb water.