According to WoB (sadly I don't have a link to this), Duralumin-Boosting Feruchemical charges is not possible.
...the WoB would be tremendously helpful in this case.
I think the idea is that if you boost your Reputation "for a single action" -- it's a single SOCIAL action, which means that it may stay boosted for a minute, a few hours, or even for days, for the purpose of that action.
Also, there are times when you need to roll against Reputation, particularly defensively, so being able to tap Duralumin for that remains useful.
Hrm. There's an interesting idea, then. Are you suggesting that you think duralumin can be tapped for defensive actions, and that when it is, it can increase my reputation while my reputation is being attacked? This will, obviously, revert a moment later, so if you're reducing me to 0 I'll lose regardless, but it would potentially prevent me from ever gaining social burdens.