You can use the following macro, it takes some setting up, but it will work just fine.
First, you have to place Holy Word: Chastise on a action bar. Then run the following macro while hovering over the HW: Chastise:
Code:
/run print(GetMouseFocus():GetName())
That will print some text to your chat window. In the below macro, replace [result of before] with the name exactly as it appears in your chat frame (Caps and everything)
The below macro is what you enter into healbot.
Code:
/target [@mouseover]
/click [result of before]
/targetlasttarget
You should end up with something like
Code:
/target [@mouseover]
/click ActionBarButton1
/targetlasttarget
(or if you're using a bar addon like bartender)
Code:
/target [@mouseover]
/click BT1Button2
/targetlasttarget
Hope that helps