How to get pre-approved for a multi-family- need rental income

[Sierra Swords]

Hello! 

I bought my first property in February and am hungry for another. I am looking to owner occupy, put 3.5% down on a two-unit, but in order to be approved I know I will need the rental income (75% of estimated) to offset the mortgage. How then, can I be 'pre-approved' to even go see a property when the rental income isn't estimated 'officially' until the appraisal is done?