Can I spread a cost around the whole month?

The best way to spread the costs out over the month is under the Monthly Expenses option on this page here.

Monthly expenses are calculated proportionally to the dates you select. For example, an email expense for November is $100. If you select November 1st to November 15 the total days would be 15. So the proportionate monthly expense would be (100/30 days) * 15 days. Leading to a proportionate expense for November 1st to November 15th of $50 dollars. Whereas November 1st to 30th would display $100.