I was looking at this thread before, thinking this pseudoscript would be neat:
But it does not really give you lots of flexibility or granularity 
does not really give you lots of flexibility or granularity
BUT! You could make the Map 100 elements long, each int is associated with a descriptor:
Then you can control which descriptors kicks precisely at which percent, with the precision of 1 percent. You could quickly make it in a spreadsheet, chuck it into the data table even. Sounds like an overkill but it would be neat-ish in a way.