Thanks to jamesw over at RailsForum.com: Same Model for Two belongs_to Associations a solution has been found.
class System < ActiveRecord::Base
belongs_to :project_manager, :class_name => 'PointOfContact', :foreign_key => 'project_manager_id'
belongs_to :technical_manager, :class_name => 'PointOfContact', :foreign_key => 'technical_manager_id'
end
class PointOfContact < ActiveRecord::Base
has_many :project_managed_systems, :class_name => 'System', :foreign_key => 'project_manager_id'
has_many :technical_managed_systems, :class_name => 'System', :foreign_key => 'technical_manager_id'
end