Clique converts your mouseclicks into healing. Like, left click is Flash Heal, right click Cleanse, mouse wheel down is Earth Shield etc.
1. Install Clique.
2. Ensure that Instant Swapping is enabled in your layout so that your mouse repeater region is synchronized across screens.
3. Make a repeater region for each of your alts which ONLY passes the mouse movement and clicks to your healer.
4. Use Clique to bind the different mouse clicks to the heals you like.
5. Profit.
Just make sure you save the mouse repeater region as Auto on each of your slaves so you don't have to reset them. Good idea to set the regions up to block the clicks from the window you're in, too--You don't want your slaves to randomly do stupid stuff
Edit: You might also consider using a focus healing setup if you want it to be even more one-button-ish. You can make a macro like:
/castsequence [@focus,exists,nodead,help] Holy Shock, Flash Heal, Flash Heal, Flash Heal
/cast [@focus,exists,nodead,help] Word of Glory
And then just set it up in Clique so that when you left click on a unit frame it sets them as the focus for your healer. Then the healer will mindlessly spam heals. You could even get fancy and set up TWO macros--One for fast healing throughput like this and one with Holy Light for light topping off heals and use two different keymaps to alternate between the two.
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