RRSPs and TFSAs are the only tax protected accounts he'll be able to access. If he has a spouse/partner who hasn't maxed out their RRSP or TFSA he could give them money and they could invest it to avoid the taxes on dividends.
If he has a business or knows someone he'd like to partner with he could invest in that instead and write off any contribution he made as a business expense.
Even if he decides to go the route of putting it into a non-registered account it's not a ton of taxes. I don't see any evidence that ZNGA has paid dividends before though, and the Trailing Annual Dividend Yield on VGR is 12.20%, so if he was making around 100K from regular income his marginal tax rate would be around 30%, so really he's only paying 3.66% tax on any money he invests in there (assuming he invested all of it into VGR). He could also look for other funds that don't pay dividends.