Is there a quantitative method to follow to determine FILLFACTOR for NONCLUSTERED INDEXes?

Question

I've read different ideas to set FILLFACTOR and then monitor fragmentation over time (#1: 5 Things About Fillfactor, #2: Database Maintenance Best Practices Part II – Setting FILLFACTOR).

Instead of making an 'educated' guess upfront and then adjusting, I was wondering:

• If anyone knew of a (quantitative) way to determine what level of fillfactor would be needed upfront?

(I'm primarly concerned with respect to NONCLUSTERED INDEXes, as I typically create my clustered indexes on ever-increasing integers.)