All you have to do is to cover and protect it from rain/snow/water washing the nutrients away from it. Compost is like wine, the older the better.
JMO

Finished compost can be kept for some time if it is kept dry so the bacteria that digest the material cease working. While many people think aged compost, like a good wine, is better that is not true since time allows the bacteria to continually digest what is there (when conditions allow them) will be eventually eaten just as it is when in the soil.