This is not possible and has been suggested many times in the past. I, too would like to see this added.
Ideally, each control which can display text should have a font option:
edit "text", id, x y w h, style (left, right, center, multi, pass, read, return, hsbar, vsbar, autohs, autovs, limit N, rich, fontname="font with space", fontsize=N)