I have this TV too. I don't know of any default buttons you can press to access your Sky Box. I do know that equipment connected to the TV via scart lead will automatically come on when switched on if the TV is already on. However, I don't know if this works for items connected via HDMI leads.
As far as I know it's not possible from the normal user setup.
It might be possible you can do it by entering the service menu, but from memory you would need to put the TV in hotel mode which would restrict access to a lot of other features.
I'll have a look tonight and see if there is anything else in the service menu that might help (be aware if you do make any changes in the service menu you do so totally at your own risk, change the wrong thing and you can really bugger the TV up!)