MPLS-TE : Moving traffic off a over utilised link?

I'm looking at the possibility of enabling MPLS-TE to start using links in our core which at the moment are only ever going to be used in the event of a failover.

We have 10Gb links which at busy times of day are hitting around 80% usage. What I would like to to if possible is to enable MPLS-TE on the core only so that when a tunnel/link is seen to go over 75% that it starts using another explicit path/tunnel over the network to the same destination.

When the usage again drops down to below 75% then traffic goes back to the regular (less hops) path.

Is this level of control possible with MPLS-TE? I know you can create tunnels with an amount of bandwidth allocated to that tunnel but can you set it up so that it only uses up to a predefined amount of bandwidth and then get it to either use another path or another tunnel?

Example

So in the example above traffic from S to D will normally take the R4/R5 route but if this is experiencing over 75% of usage then all new traffic will go via R1/R2/R3 until the traffic again drops on the shorter path.

In case it helps it's a BGP free core running OSPF. PE routers are in a iBGP/MPLS VPN mesh.

Thanks