Tried to find reference to Transform Scripts which describe how to do Latin 1 Supplement diacritics/composites. Found all sorts of other scripts, such as Cyrillic, Discretionary ligs, Eastern Europe, Greek, Letterlike, etc.
Weird request, but it’s been a while since I added these so at best forgot how to do it.
If your font already contains glyphs for A-Z, a-z, and the accents (you will need acute, grave, diaeresis, circumflex, ring above, tilde, and cedilla)¹ then just select the Latin-1 Supplement glyphs except those that are not empty, and use Complete Composites.
After completing composites, you will need to do some editing² on Æ, æ, Ø, ø, Ð, Þ, and þ, and create suitable glyphs for ß and ð.
¹ Generic accents are included if you use “Include Outlines” when creating a new font.
² See Adding Æ and æ to Fonts for some tips on combining contours.