How to add a billable item to an exsiting invoice ?

Hi,

I have a client who ordered 1 domain name couple a weeks ago

now he want an hosting, he agrees to pay for the hosting at the same date that the domain name was issued.

I know that I can ad manually the item "hosting" to his invoice but

I 'm wondering if is another way for adding a product/service already defined to an existing invoice

thanks

p.s. I'm on the 4.2 version