I believe there is zero chance of getting a Motability advisor to extend a 3 year lease.
They can extend for a max of 4 weeks, but only during the last 2 weeks of the lease! They told me.
The people to speak to is a member of the grant team. They and they alone can extend the lease for a further 2 years.
I’m unsure as to what circumstances they would agree, but it must be worth a try.
Knowing what circumstances would be really helpful.