I play a sage, full champion pvp gear etc etc. Sadly healing alone will only yield ~3 medals +/- 1. I can routinely get 6-7 as long as im not getting extremely focused. Although to do this you have to heal 300k+, get the 5k heal (usuallly pop cooldowns and relics and heal self to get).
In addition I dot EVERYONE, if they die you get credit for the kill. Also watch for guys to be low on health and try to kill them to get a medal for that. You should be able to rack up 2 medals for defending if ur fighting near the cannons.