I don't think you can have IS Boxer focus the camera on what the priest is looking at.
There are five definable views, and you can switch between them via macro.

You could lead with the healer.
Briefly press your formation key, which has everyone move a little (and breaks follow).
Then hit a mapped key for IWT, which only sends the keybind to the tank (or tank + melee toons).

Possibly switch to the tank window (set it IS Boxer so you don't auto-follow on a switch), if you need to position the boss or change its facing.

Then hit your DPS/Tanking rotation (from the Healer's window).
And possibly go with special abilities on the tank, like Taunt etc.

Zanthor's video series "Expanding the Possibilities" shows him driving with a Resto Shammy.
And has a tank and rogue on the team.
So driving the healer is very doable.