I won't be in the UK or have internet access from Monday onwards, but if someone in the UK (i.e. preferably serotone or hys) rings the UK visas and immigration center on 0300 123 2241 or 0800 389 8289 (Mon-Thurs 9-4.45, Fri 9-4.30) they should ask them whether "proof of donations received to attend an event" counts as demonstrable proof that he will be able to fund himself in the UK and explains the team situation. You can also argue that he effectively earned the donations by playing the game well and practicing which might work on a technicality.
Idk if you've given sdb the money from the fundraiser already but if you pay it into his bank account as a transaction it would probably make the proof stronger. I'd also say include info about the fundraiser and the individual transactions into the account of whoever was organizing the fundraiser (HYS?).