how to send proforma invoice before payment is received?

[RudiAhlers]

Hi, 

Can someone please tell me how to send a proforma invoice to a client, before he makes payment? And then to manually send the TAX invoice once payment has been received?

My store only accept manual payments - i.e. bank transfers. 

[Erlebnisfabrik]

This is a nice question. Is it possible without an plugin?