If you want to use the cash basis accounting method with FA, all you need to do is change the "Accounts Receivables" account group from an Asset to an Income account. The Profit and Loss and Balance Sheet reports and tools will then report on the cash basis. Its really that simple.
This should suffice for most simple businesses. If you offer customer financing or prepayment, it gets a little more complex, because you may want to split interest from sales because of reporting requirements, and have to deal with negative A/R. For example, customer A prepays $100 without an order and customer B makes a $100 order but hasn't paid yet. Is your income -100, zero or $100 using cash basis accounting? Good question on an accountant exam.
Caveat: this technique is broken if you use dimensions until FA is updated with a pull request I made.
If you use Accounts Payable, you would have to change it from a Liability to an Expense account (I haven't tested this).
Note: you can change the account group of "Accounts Receivable" back and forth with no harm done if you want to switch between cash to accrual basis.