Is there a way of doing a manual EFT payment without a vendor being set up? Or even if a vendor is set up, but you only wish to run a single payment by EFT. Is there any way to do this in A/P?

A vendor is required to store the vendors banking details.

Single cheques can be done from a manual cheque batch.

As Doug says, you need a Vendor because that is where the banking information (account, institution etc) is stored. You could use a "MISC" vendor and keep changing the banking information each time but that would require very great care otherwise payments would go to the wrong vendor. Your ability to track down the banking information for past payments would be very limited. Besides, do you really want to ask a one-time vendor for their banking information?

I would not recommend this. It's just a string of numbers and it would be way to easy to send the money to the wrong bank account.