You can definitely make a support build for Sunsinger. I know that Song of Flame is pretty underwhelming most times, but it can be very supportive with the right team. Radiant Skin is a great secondary option (especially used with The Ram) as you can tank enemy attacks and hold their attention away from the rest of your team. Don't forget that Fireborn can literally save teams from wiping. If that's not support, I don't know what is. That was just the basic super tree; let's move to the melee. There is a perk that, if you're sort of lucky, can generate two orbs per charged melee kill. Use this with Claws of Ahamkara and that's potentially 4 orbs per double melee. Honestly, all other perks are simple utility perks that mostly benefit the Sunsinger alone. However, the class itself is so versatile that you can use it for almost any role you'd like. I personally use it in a support role with Radiant Skin and the orb generating perk. I sorely miss my Sunbreakers, as those made Solar Grenades an amazing support tool.