How to record prepayment on an hourly project

How to record prepayment on an hourly project

I had a client pre-pay for a job. I have no idea how to record this payment in Zoho Books. 

This is an hourly project. For hourly projects, in order to record a payment, I think I have to create a project, create a task, log some hours, create an invoice then record a payment. 

Oh, wait, here's an idea. I don't know if it will work.
  • create a project, 
  • create a task, 
  • log some fictitious hours, 
  • create an invoice, 
  • record the payment, 
  • then log in some negative fictitious hours.
That way, when I am done I will have recorded a payment for an invoice, and I'll have zero hours. For this to work, Zoho Books will have to show that I owe the client some money/hours, which gets zeroed out when I actually do the job and log in the hours.

That seems like quite a lot of hoops to jump through just to record a down payment on a future job. Anybody know of an easier way?