Topic: Adding Funds to Xbox Account with Pre-Paid Card?

I recently got a pre-paid Mastercard as a 'gift' when changing my mobile contract. I've already spent most of it, but there's a small balance left. I was hoping to just add it to my Xbox account balance, but couldn't find a way to do so - the website only lets you buy certain values of gift card to add to the account.

Is there a way to add funds to the account direct from a card?

So, it would seem this isn't possible - I ended up just adding it to my Amazon balance instead.