Hey moe, I'll shit in a bag and mail it to you fourth class. By the time it gets there it will likely have composted! 
Papa, you could stretch it if you want to. Why worry? You're so close now, why risk another step? Not too mention that compost benefits highly from the nutrition of a heavy spawn rate. Stretching it now would lower the overall nutritional value by diluting the spawn. Four gallons of compost should yield heavily. I wouldn't be greedy.
Not to mention four gallons will fruit for a long time. Keeping you in stock while you start anew.
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-From a registered Mad Scientist
"From a certain point of view"
-Jedi Master Obiwan Kenobi (also a Mad Scientist tm)
VisitThe Donkey!-just behave