The 28-year-old Lapierre had four goals and six assists in 48 games with Vancouver, and appeared in four playoff games. The 34-year-old Aucoin had six goals and six assists in 41 games with the Islanders.
St. Louis also signed forwards Mark Mancari and Alexandre Bolduc to one-year, two-way contracts coming off high-scoring seasons in the AHL. The Blues drafted Bolduc in the fourth round in 2003.
The 27-year-old Mancari had 61 points in 76 games at Rochester, while the 28-year-old Bolduc had 51 points in 56 games for Portland.