How do I arrange creative low interest financing for a partnership buy in?

I have an offer to become a partner in a successful business that nets $150k per year. I need to put up $550K now or $375K now and $375K later when the other partner retires. There would not be enough yearly net return to pay both partner's wages and a loan payment on $375K or $550K at an 8% commercial loan rate for eight years. I have $800K currently in an IRA that would be taxed highly plus penalized at a 10% rate if I were to use it. How do I creatively finace or leverage my IRA in an effort to buy in?