There are many ways to go about this, here's one that you can do pretty quickly:
Example: Sorting Customers by Sales
1. Bring out Sales to detail
2. Add a quick table calculation for rank
3. Change it to be discrete
4. Add it to the rows shelf
Now, if you filter out a few employees the rank still works and will move up the next person in line.
To add the Top N feature, create a new parameter and create a calculation saying rank is less than or equal to your parameter
I've made a quick video that shows how to do it.
Let me know if this helps!