The only way to gift credits to someone is to buy one of the gift cards that WGT accepts to buy credits and give then the gift card. The cards accepted are Subway, Burger King, Circle K, Dollar General, Shell, CVS, and Sports Authority. There is one more but I wasn't able to tell what it was just by looking at the top of the card shown on the news page.Actually you probably don't even have to give them the card, just the number off the back of the card.
Much easier than playing any of the chaallenge matches and losing.