You have two simple options:
1) Create new process instance dynamically based on the % that you have for a specific instance. So you will end up having multiple rules that evaluate different values of the % and based on that create a new instance of a specific process.
2) you can have a complex gateway that select a different path depending the value of the %.
The third but more complicate option could be:
Create dynamic Human Tasks based on a rule that evaluates the value of the %. This task will be created dynamically and using a Complex Converging Gateway you can wait for all the dyncamic task to be completed.
I don't have any example of this, but if you have a specific use case I can help with the solution design. If you want to share your use case privately go ahead and send me a private message.. if you can share it with all I will be glad to help.
Greetings