URGENT - Priority with no SLA required

Our IT department requires all types of requests to be logged - including projects and internal routine processes. Projects in particular will never have an SLA as they may get logged and sit on the shelf for months before pulled down to work on the next phase - then be shelved again until resources are available. How can I configure SDP to have a Urgency/Impact that sets no SLA for the Priority Matrix? This is wreaking havoc with our reporting back to senior managment because we have to keep telling them to ignore the Due Date. They also do not want us to create some artificial due date in the far future to get around this.

There is a lot of urgency around this as there has been a large shakeup in the senior management here and the new management is not giving us a lot of time or leeway in trying to resolve this.