Is there a way that I can pay less for taxes on my commission earnings?

No. You will be charged 25% tax on all commission/bonuses no matter what you put on your W4. If you will have paid too much taxes by the end of the year, increase the allowances (?) on your W4 so that you pay less taxes on your salary. But be careful. If you end up owing too much, you will have to pay penalties and interest in addition to your taxes.

If you are an employee, you need to run a dummy 2015 tax return. Commissions are usually not considered paychecks and have income tax withheld at a flat rate of 25% for federal. If your income is so low that you don't even reach the 25% tax bracket, you won't owe this much when you file. To compensate you can increase the number of allowances on your W-4 for the regular income.

if you are talking about the amount withheld on your one time pay check, probably not, this is not based on how you filed your W-4 but based on a one time payment which is more
however when you file your tax return and more has been withheld than you owe, you will get it refunded to you
you can also consider the credits you are allowed to reduce your gross income, ie contribution to an IRA

No

There are many ways to pay less taxes on commission earnings, just like with any other type of income. There are so many tax deductions out there that I'm not going to bother listing them out here, but you could look into donating to charity, deducting mortgage interest, or going back to school.

Of course, if you are just looking to reduce taxes without doing anything, you are probably out of luck. If I were you, I would use tax preparation software such as TurboTax or TaxAct next tax season as these are good for making sure you maximize your deductions and credits.

Yes, don't declare the earnings. Or under declare them.