Copy the text sample you'd like to fulfill to your clipboard. Run this script. Font overview will add more template glyphs for the glyphs you still need to draw.

addMissingGlyphsFromClipboard.py

# menuTitle: Add Missing Characters from Clipboard Text

import collections
from glyphNameFormatter import GlyphName
from AppKit import NSPasteboard, NSPasteboardTypeString

f = CurrentFont()
templ_gs = f.templateGlyphOrder

pasteboard = NSPasteboard.generalPasteboard()
text = pasteboard.stringForType_(NSPasteboardTypeString)
text = text.replace("\t", "").replace("\n", "")
counter=collections.Counter(text)
letters = "".join(sorted(counter.keys()))

for letter in letters:
    gn = GlyphName(ord(letter)).getName()
    if not gn in f.glyphOrder:
        templ_gs.append(gn)

f.templateGlyphOrder = templ_gs