Requisition Self Service - Workflow

Has anyone customised workflow so that it skips levels of authority limits.  For example - we have a requisition of $28,000.00  and the limits are set by distribution list, with app 1 limits being $5,000 approver 2 limts being $10,000 approver 3 being $20,000 and approver 4 $50,000 and above.  We want the workflow to point directly to approver 3.  we have tried unsuccessfully to do this within the standard workflow.  is this a huge effort to customise the workflow, or should a whole new workflow be developed to do this and replace the standard workflow.  on version 8.12.