Set up a delegated approver for the manager is the recommended solution to ensure all of the appropriate deals are reviewed and the leaderboard is up to date. According to the Salesforce documentation, "A delegated approver can approve records that are submitted for approval by users below them in the role hierarchy." Forwarding the approval request to the manager's assistant, having the manager log on and reassign the approval request, and using Process Builder to assign a delegated approver are not valid or feasible options.