Does it have to be in a gift card format? If you are doing it via gift cards to MS that is fine, but maybe the best idea is to create a new e-mail and then use a money sending service for the payment since the e-mail is ehat the recepient will see. The name can be ''anonymous donor' or etc. Of course, if e-mail limits the possible # of people that might be gifting more than a mailing address then this approach might be moot.
In a recent deal, Staples was selling $100 MC gift cards. That might work for your purposes. They arrive via US Mail. There might or not be fraud associated with these particular MCs, so buyer beware... I plan to liquidate mine as soon as they are activated.
Looking at it from a different POV, if the person is spending above their means for whatever the reason, a VGC might not be the best idea. Just my 2 cents.
Edit: Amazon also sells $100 VGCs