I'll add this for the OP: If your employer is small or medium sized, it's theoretically possible that you could convince your company to add profit-sharing contributions to your 401k plan. The conversation could go something like this:
"Mr./Mrs. Senior Executive, has our company ever considered adding profit-sharing to our 401k plan? It could be a major tax benefit for both the company and for all of our employees, you and me included. Instead of paying out our full bonus amounts as cash payments, we could pay out the first X% of each employee's salary as a profit-sharing contribution.
Example: Let's imagine our company decides to give all employees a flat 3% profit-sharing 401k contribution this year. Jeff's base salary is $100,000, so he would receive $3,000. Under our current bonus structure, Jeff would have received a $12,000 cash bonus this year. Instead, the company can give him the $3,000 profit-sharing 401k contribution and a $9,000 cash bonus. The $3,000 would be tax-advantaged for everyone involved. Win-win, amirite?"
[Edit: typo]