The move became necessary when star kicker/punter Swayze Waters was injured in the Argos' season-opening 26-11 victory over Edmonton in Fort McMurray, Alta.
Toronto announced Tuesday that Waters, the CFL's top special-teams player last year, will miss the next four-to-six weeks with a tear in his hip flexor.
Pfeffer, a five-foot-11, 185-pound native of Kitchener, Ont., recently attended training camp with the Ottawa Redblacks.
In 32 games over four seasons at Wilfrid Laurier University, he punted 278 times for 10,010 yards while adding 7,159 kickoff yards.
The two-time OUA all-star and 2014 CIS all-Canadian also converted 57-of-81 field goal attempts with a long of 50 yards as a Golden Hawk.