You can hold the bolt partially back touching the hammer and pull the trigger. The hammer will just follow the bolt as you let the bolt go forward.
No need for a snap cap.
From a physics standpoint there is no need to release spring tension before storage of any rifle. Springs do not lose force by being stored in static compression. They only lose force through repeated cycles of compression and decompression. Therefore you are actually doing more harm to your rifle than good be releasing the spring tension. However, in either case, the spring will probably outlast your natural life.