I've taken the mapped keys: FTL Target Me and FTL Assist Me.
And copied each five times.

The copies are then edited, so the target is changed.
Instead of: Windows All Without Current, they are Slot 1 (for #1), Slot 2 (for #2), etc.

So I now have:
- Slot "x" target me.

And:
- Slot "x" assist me.

If I want a Rejuvenation round-robin...
I can make a ten step mapped key.
Step 1 is "Slot 3" Target Me (run by Slot 1).
Step 3 is "Slot 3" Target Me (run by Slot 2).
Step 5 is "Slot 3" Target Me (run by Slot 3).
Step 7 is "Slot 3" Target Me (run by Slot 4).
Step 9 is "Slot 3" Target Me (run by Slot 5).
Step 2, 4, 6, 8, and 10 are: Send Keybinding for Rejuvenation to Slot 3 character.
You can include a "Do Not Advance For At-Least", on the steps to account for latency or casting something else.
You could also take the last step, and set it to not advance for 9000 seconds... but set the entire mapped key to reset to Step 1, after "xx.x" seconds from the first press...
(This assumes your healer is a Druid, and is in Slot 3).