How to give variable salary to director of OPC ?

How to give variable salary to director of OPC ? I understand basic salary should be constant. This month, salary would be set at 50k inr, Next month it might be 2,50,000 inr. Basic salary might be set at 20k inr.

Can i give variable incentives throughout the year ? What should i call that incentive ? OPC does export of service -- website advertising to foreign clients in usa.

Thanks sir  and madam  :)