"he is still considered self employed even though he draws a W2 every year."
If a sole-proprietor is issuing himself a W-2, he's doing it wrong. A sole-proprietor does not receive a W-2. Only the non-owner employees of a sole-proprietorship receive a W-2 and those employees are not self-employed with respect tot he sole-proprietorship. The fact that a sole-proprietor has an EIN does not change the fact that the sole-proprietor is not to issue himself a W-2.
Perhaps you misunderstand which form the business will be issuing to you. If you are truly an independent contractor, the business should be issuing to you a Form 1099-NEC to report non-employee compensation, not issuing you a W-2. In that case you could establish and contribute to a solo 401(k) and TurboTax would accommodate that by allowing you to claim a self-employed retirement deduction. If you contribute to the traditional account in the solo 401(k), the self-employed retirement deduction that you receive effectively converts your after-tax money to pre-tax (tax-deferred) money.
