a long while back on Feenix WoW 1.12.1 Emerald Dream, there was a user who posted a link to a Classic Mouseover addon that let you cast spells by hovering your mouse cursor over a nameplate of a target. It didn't have the full function of the later retail WoW client that let you do a mouseover cast on a target by hovering your mouse over their character's head, but the plates were good enough for me, especially in raids.
The link on their forums went down. This is a fresh upload of the addon.
The macro command is "/cmcast Regrowth(rank 1)" or just "/cmcast Regrowth" for using your max learned rank, using the Druid spell Regrowth as an example.
http://www.fileconvoy.com/dfl.php?id=ga54e4072c252c0c99999634570e0dc07f5fa4721f