Add contingency to task

Has anyone thought of a clever way to add a percentage contingency to a task?

Say I have a resource assigned to the task with an hourly rate attached but our confidence of that task completing in the given time is low and there’s a good change it will take 25% longer and the cost will therefore be 25% more. I need to capture the 25% in either the duration or the hourly rate (but only for that task).

Just to be clear I can’t just up the resource’s rate by 25% because then every other task I attach the resource to will cost 25% more. Creating 2 personas for the resource at different rates breaks the levelling so that’s out too.

you likely won’t get an answer here, there is very little traffic

does running a Monte Carlo fit what you are trying to do?

I don’t have an elegant solution. I would simply add a second task, with the extra 25% time & cost and make it dependent on the original task. Crude, but it would work