It wouldn't be too difficult to make it a one-time-per-day refill of as many kegs as you've got. I think that's the way I'd probably do it.
Do full kegs that are used just disappear, or are they added back into your inventory as empty kegs?
I should likely know this, but have never really given it any thought before.
(I just tried, but I have no advy hours left and the keg I used did not empty after 4 uses. Any other time I am lucky to get 2-3 uses per keg)
_IF_ the used kegs go back into inventory as empty kegs, I believe that there would be more room for possible abuse.