You can mark other players with the same marks you use on monsters. When you're solo, no one else sees your marks. So you can mark players with the numbers 1-5, bind 1-3, cross, circle, X, square, etc.
You can then use <attack1> - <attack5>, <bind1> - <bind3>, <Stop1> - <Stop2>, <square>, <circle>, <cross>, <triangle> etc. to target those players with macros. For example: /ac "Cure" <attack1> to cure the player marked with the number 1.
See
the manual for more information.
I think if it were me, I'd double up with the party member macros like so:
/ac "Cure" <attack1>
/ac "Cure" <1>
But I haven't tested this kind of thing, so I don't know how that would act with a hostile target marked with 1. It might fail in a different way than out-of-range or nonexistent target errors, so it might not fall through to curing party member 1.