Originally Posted by
[-Spiritus-]
Yes, but its kinda tricksy.
(1) Make sure both SelfCast options are off.
(2) Place Holy Word: Chastise on your hotbar.
(3) Mouse over said hotbar button and copy "/run print(GetMouseFocus():GetName())" in chat and press enter.
(4) Write down the result of the script (you'll see it in chat).
(5) Create a new macro called "HW" [or w/e] with the following script:
#showtooltip Holy Word: Chastise
/target hbtarget
/click INSERT_STEP3_RESULT_HERE
/targetlasttarget
(6) Open mouseover addon of your choice [healbot, vuhdo, clique, etc.] and type in "HW" [or w/e your named it] in the button you wish to bind it.
(7) Make sure your chosen button is not bound to anything else.
You now will be able to mouseover with Holy Word: Serenity. Basically, by doing this, you've bound the hotbar button instead of the spell to your selected key, which allows for the mouseover to be valid. The catch is, to cast Holy Word: Sanctuary with the same bind, you must first be moused over a valid healing target. To get around this, bind Holy Word: Chastise to another button and use that exclusively for HW: Sanc.