I tried this already. they locked my account with $4k usd worth of giftcards in it. wasn't able to get that money back
Which service was it? See my post above, I added a link.
Also, how much are you planning to buy exactly? If it's going to be thousands per day, then I'm afraid no service is going to help you, even if you use multiple providers, you will still have to deal with the monthly limit.
Your best best would be to buy from other individuals on the forums.