mechanical timer and wired stat?

[Matty Birch]

have had a customer on the phone this morning wanting a wired stat adding to an eco elite that's currently controlled of just the mechanical timer, never had this requested before as it's usually a programmable thermostat I'd fit but I can't see how this would work as the switched live is already taken for the timer. Anyone a bit more clued up able to offer advise.

Thanks in advance.

 

[ShaunCorbs]

Honeywell 6360

And yea 3 core cable from the prog to the stat