Giving up coins is part of being an Outlander. Just get some valuable item and find wildernessy enough merchant you can barter your booze from. That would work role-wise well for a true Outlander that is a drunkard, not a ####ty on purpose Outlander who shouldn't get inducted.

And yes, I'm 100% sure that it's hard coded that you cannot buy stuff as Outlander. I have typed in the 'b'-command as Outlander (though not trying to actually buy anything). It gives you an echo that the thought of currency sickens you or something. Carrying coins makes you makes you lose unbound spirit and using items marked with gray taint flag plaques you and makes you lose cabal powers for a duration of time.