Early 'unicorn' employees can't always cash in

Problem: employee can exercise the options, but must do so immediately and must pay tax on them when they are exercised. Employee can NOT sell the shares now.

Solution: Provide the employee with a loan sufficient to cover the tax burden (to reduce risk, make it no MORE than enough to cover the tax burden), which is guaranteed by a lien on the shares. Employee still owns the shares, and the company making the deal must shoulder several risks including the risk of the stock price falling, but can charge enough to make up for these risks.

With such companies there is often a large interest in purchasing shares which the market cannot satisfy (because the shares are not available publicly), so perhaps you structure the deal so that the loan gets paid off in SHARES instead of dollars. Then the lender could finance it from people with an interest in the shares.

Would this work? If not, why not?