honestly... adding such a thing would defeat the purpose for Challenge Log. it's there to get players to expand the things they do. instead of just doing the same thing everyday. it's designed to encourage people to do new things. i am sure there are other reasons too. like for players that don't have the time to do something repeatedly all day. it allows them earn EXP and gil from other sources that can be completed by doing simple daily tasks.

and if you want EXP for a class/job... then you should be playing it to start with. heck i do the leve quest and FATE section with a THM. i expect it to be 50 in no longer then 30~45 days. if you are trying to go quicker... then you are going to need something more then just the Challenge Log anyhow. it's not some kind of power leveling system you can use to just dump EXP where ever.