The website will have 1) His history/ current situation/ goal. 2) A set monetary goal and its uses - and an online counter. 3)Donation page and download of free content (art by him or coupons from near by establishments. What would move you to support and donate? An awesome website? A great video? Really fun perks?
Any donation using a Web site and QR code will eventually create a tax liability for your homeless friend along with the obligation to share a percentage of any incoming donations with Paypal or similar companies, but the real challenge will be to convince a bank to open an account to withdraw funds. I also feel that a homeless using QR code and a Website to promote itself could be ill-perceived as a marketing strategy rather than as a mean to survive, although your intentions to help this person are very noble and sincere.