Here is my idea and was wondering if any have tried this.
Basically set up a DPS macro. Only every spell in the macro casts at your focus target.
To get a focus, use something like this macro
/assist Prissywynd
/focus
/targetlasttarget
So you would put the name of some DPS person who knows how to stay alive in your focus macro, the macro would assist them, giving you their target, set that to focus, then return to your last target. Thus you could hit this macro, and it would give you the new target that DPS is focusing upon, and you would then mash out your DPS macro.
What this would then let you do is click on the party/raid frame and heal anyone else, all the while going back to DPSing the main target.