Whilst creating custom matches on the needed peaks DOES NOT count towards this achievement, having a boosting partner create ones for you DOES (I've just confirmed it working). This is fortunate as the DEVS are now only holding events on 2 mountain ranges a day and they sometimes don't even include all the peaks.
You and your boosting partner can only create 3 custom matches at one time so set them all to 10 mins each, quit out when it loads up and then move to the next mountain range once the timer expires. All the ranges (Africa / Alaska / Alps / Antarctica / New Zealand / Patagonia / Rockies / Siberia) have 3 peaks apart from Himalayas which has 4 so I would leave this one until last.