What about keeping the PM, but making Milliband the face of the party

I support labour. But here could be a tactic for labour to counter the youthful leader the Lib Dems and the Tories have.
As people seem to prefer younger leaders, but want the experience of an older leader.
What about keeping the PM but appointing a young statesman such as Milliband as a sort of deputy PM who can be the face of the party obn TV interviews, party conference, speeches, debates, politcal broadcasts etc:.
That way you get the benefit of an experienced PM, but with the young fresh face as the youthful face of the party.
The previous PM used the present PM to make up for his lack of skill in some areas of politics. Why can the present PM not use someone to make up for his lack of youth.
My idea would be swap Darling for Milliband so Darling does lose face he would still have a high profile job as foreign affairs Secretary, then appoint Milliband as a powerful chancellor, maybe even with other portfolios such as deputy PM or more likely First Secretary of State. Then send him on TV as the face of the party on TV, to clear up the issues the party has to face.
That way you do not have to go through the trauma of the party losing a leader.
You also get the advantages of the present PM's
1: Experience 2: Tactical ability 3: Economic competence & reputation.
Yet you can sincerely put forward a youthful face for the party as Milliband as chancellor would be powerful and show there was a young leader in the party.