The closest thing to what you are looking for is a Pyro with 9 points in Bodyguard.
Take Pyro to the top level, only using 31 points. In the bodyguard tree take the talents from the bottom 2 tiers that decrease heal casting time, and increase heal percentage.
This is actually a viable spec for unrated warzones. You can still dish out 90% as much damage as a full DPS Pyro build. The only difference is that you lack a couple Power Shot talents so you won't be using it as much, if at all. (Normally you would take talents to decrease Power Shot channel time as well as pushback, but you took these for heals instead.)
The healing you have will be great as off-heals. You will even be able to heal through damage against only 1 moderately geared player. Any more than 1 person on you and the heals are useless.
But the true healing value is when you are left alone. Your Rapid Scan will heal for just as much as a Full Bodyguard's heal, and will channel just as fast. So you can play as a DPS, but sometimes you can step back and be a very strong healer.
Can you post your build? I am new to merc and this sounds interesting. I have only done a few flashpoints and have found the need to self heal a few times.