Liquidity for early employees

Early employees at fast growing startups often have the vast majority of their wealth tied up in stock options. Unfortunately, until an exit, they have little to no liquidity. And even when there is a liquidity event, they may not be able to afford the taxes incurred by exercising their options.

While I understand why investors want employees to continue to be incentive aligned with company growth, it feels like there should be a way for early employees to get some liquidity earlier. Founders can sometimes negotiate to sell some of their shares during financing. What tools can early employees use?

I'm talking with a friend who is considering trying to take a loan from an investor at a steep discount using his locked-up shares as collateral. Are there other creative ways for him to get liquidity without signaling risk?