Actually what I'm doing right now for 99 fletching seems like the best way.
AND ITS FREE, actually makes a bit of profit.
For every 150,000 fletching XP you want, buy 1000 yew logs and 1000 bow strings off of the GE.
Make 1000 yew longbows (strung of course), and sell those.
You will receive more gold than you spent on the logs and BS, and you will have gotten 150,000xp in fletching!
I've been doing this for about 3 days now and I've gone from 74 fletch to 83 fletch.
I should be hitting 86 today.
I should be 99 within 10 days if I do this for about 5 or 6 hours per day.
It takes about 1 hour 15 minutes to fletch 1000 yew longbows.