I bought an iPod Touch app and want to use it in my wife's iPod

I just bought an application from the App store and I want to upload it to my wife's iPod Touch. However, my iTunes account is different from hers. I read in the terms of sales that the app you buy can be used in up to five different devices. How do I upload the app I bought in my account to my wife's iPod (which has a different account)?

Thanks!