I agree that a mega-backdoor Roth is a potential approach, but to be clear, there are a LOT of hurdles that your 401k administrator has to jump through to allow this, so it's an example of an "if you're lucky enough to have an amenable 401k provider" suggestion, not an "everyone should do this" suggestion.
Angel investing from a Roth account is a more universal possibility; not all Roth administrators allow arbitrary investments, but you can roll over Roth balances to an IRA that does all this.
