Contributions to the governmental 457(b) that reduce your taxable income can only be made as elective deferrals from your pay from the governmental employer. If you want to make contributions to a retirement plan based on your separate self-employment income, you'll need to establish a separate plan.
If you are not already making the maximum permissible elective deferral to the 457(b) at your governmental employer, you can potentially increase your elective deferral there to reduce the amount of taxable income from your governmental employer to reduce your overall taxable income.
