40 F is around 4.5 C, so typical fridge temperature. Once wrapped, they should continue to ripen at 40 just fine. It will slow it down, but this can be a good thing as it helps prevent slipskin. 50, which is around 10 C (or typical cave temperature) will work too, and they will ripen more quickly, so you have to be quick to correct any indication that things are going wrong. I've ripened the few white mould cheeses I've made in our regular fridge (once I had full coverage) and they turned out fine. So, it won't prevent ripening.