This will make a massive difference, as you will essentially be seen straight away, and the actual EK rep at the airport isn't too far away usually. They also tend to be the more experienced check in agents on the F desk at outstations, or at least in my experience.

I arrived 3 hours early for EK8 last week, and was in the lounge - absolutely not drinking alcohol - at 6.30am after a stop at Boots.

I don't have any experience of checking in what you are suggesting, but I cannot imagine it will be something new for the team at Heathrow, but you never know!