I wanted to do something like that, but it was a lot of work and I gave up mid way
What I wanted to do is:
add the abilities I wanted to an action bar for each character.
add a vfx source over each character's action bar.
add a dxnothing* window and have add 5 vfx viewers to it - for each of the vfx sources. order them in the same order as the characters in your party (so your party needs to be sorted the same regardless of the toon you're playing)
add a vfx source over the five viewers and a vfx viewer of that source to your actual game windows.
also need to add repeater regions for the viewers so your clicks go to the original window.
i didn't get to implement all of it so not sure if chaining viewers and sources like that actually works


*need to use dxnothing since you can't have a viewer for a source of the current window. my solution was to go through dxnothing. again, not entirely sure it works.