Manual Checks
You can pay vendors without first entering a bill by using the Manual Checks tool (Expenses -> Checks -> Manual Checks). This one-step process will let you select expense accounts for the payment without requiring you to create a vendor bill first and then, separately, a payment.
Manual Checks will ask for an Invoice Number, but it is not required to enter one. If you enter an Invoice Number that has already been used, a warning message will appear to let you know the number already exists in the system for the vendor.
After you have created the Manual Checks payment, you will not be able to make edits. You will first need to void the payment by going to Expenses -> Checks -> View/Cancel Checks, and void the bill by going to Expenses -> Vendor Bills, then you can write another check.