Turns out you can do this very easily. Just installed the Alexa skill for Mercedes Me and works rather well.Yes sounds a bit mad but wife just asked to warm the car up on the M-Me app and joked can we not ask Alexa?
But it's not such a daft question in a way. I'm guessing as MB have their 'Hey Mercedes' system then the answer is likely no. But I thought I'd ask anyway .... it would be nice to go "Alexa warm the car for me please"
So I just turned on the pre heating, checked the miles it can do and where the car is. Very simple in fact. Worth to do.
Bit surprised this wasn't mentioned at car hand over, it works very nicely with no down side I can see just now.