Use vesting which will allow you to hire him now without writing over a significant chunk of equity to him before he has proven himself. In a scenario where two

Use vesting which will allow you to hire him now without writing over a significant chunk of equity to him before he has proven himself. In a scenario where two people are "equals" (more or less), vesting should usually be done for both. However it seems like you are (or want to be) the "employer" or at least the "senior" founder here and he is the "employee". And if he agrees to this take on things, he may be agreeable to doing vesting for his share alone.