What options do I have to purchase a play store app for another account? Recently my wife gave birth to our son and I purchased the tinycam pro app to use with my d-link DCS-932L as a baby monitor.

After some tests I was satisfied with the results and decided to buy the app for my wife's google account, so she can monitor our child with her own phone. It was a surprise when I found that google provides no simple way to achieve such a simple task.

My wife has no international credit card, and even if she did I would be reluctant to associate her google account with one, since she's very careless regarding account/password security

What options do I have to install the app on my wife's phone without adding credit card information to her account?
Another solution would be to buy some Google Play credit you enter the code you buy into your wife's play store, and you can use that balance to buy apps