I've been reading Harry Turtledove's fascinating picaresques, the "Hellenic Trader" novels--historical fiction set during the wars of the Diadochi. His characters frequently carry oboloi (and perhaps tinier bits such as tetartemorioi) in their mouths, and "spit" them out to hand over to messengers &c.:
“While Sostratos eyed the dockyards and the bills and mused on world affairs, Menedemos briskly went ahead with what needed doing. Like a lot of Hellenes, he carried small change in his mouth, between his cheek and his teeth.”
Excerpt From: H. N. Turteltaub. “The Gryphon's Skull.”
I agree with other commenters here that this seems remarkably improbable (and uncomfortable and unhygienic) --is there no evidence besides the possibly satirical allusion in Aristophanes for this practice? One of Turtledove's characters is very fond of Aristophanes, so perhaps this is a meta-joke of some sort!