You can prepare a separate sales commission agreement.
Many states have laws that are very protective of manufacturers reps commissions.
You can include an express provision dealing with such sales commissions into your brokers agreement. You can be careful to make sure that the language used to cover the commissionable sale of the business. I have done this before where the goal was to optimize the signability of the agreement while still making sure everything is covered For more ideas on the provisions that you would want to include, I recommend you read Sahakian's Key Partnering Checklists. It contains every way you would ever want to structure a sales commission agreement. I ve provided the link below for you to learn more about the Checklists.