Following an employers instruction to achieve a 2 year saving on the programme - I am investigating commercial means to incentivise the contractor through the contract.
I would recommend that you have a look at clause Option C Clause 63.11.
Under this clause if the Contractor proposes a change to the Works Information any cost savings are shared equally between the Employer and the Contractor through the pain / gain mechanism.
This is a great clause to use to incentivise the Contractor to identify cost (and time) savings.
Dave’s answer is a good starting point but only if the incentive share mechanism has been set up properly.
You could bring in X6. I know you would usually do so at the beginning but no reason why you cannot do it mid-contract, you just need to be careful how you do it.
If you are already in an Alliance then you could try bringing in a modified X12, particularly X12.4 and the incentivisation of KPIs.
No option is going to be easy I am afraid so you need to look at what you want to achieve and then the best way to implement that. Sounds to me like you need to take some specific advice on this one once you have the theory sorted as the implementation could get complicated.