..best way probably to trade him in for a 4WD. Even if you had them side and work from one side to the other - anything else is anyway humanly impossible although you may understand that word humanly in a different way. These things turn into nightmares quite quickly or into one of these 6 years projects you get sick over - or even die -after spending a king's ransom, getting divorced etc. I've done a lot of conversions in my life far less complicated - at least prima vista - like diesels to gasoline or opposite, automatic to manual none of them however on a Hoe. But my conclusion is - no kidding - it is tree times the effort than you think even after a solid check and planning you cannot do this for your best friend or a customer, only for yourself. And on the end you make it up in denial.
How gold plated can your 2WD be that you do not sell and buy a 4WD?