There are vowel signs that attach to the left, right, top, bottom or wrap around the preceding consonant. You could maybe emulate it by manually placing charact

There are vowel signs that attach to the left, right, top, bottom or wrap around the preceding consonant. You could maybe emulate it by manually placing characters into a grid, but that would be very much not Unicode. Anyways, if you could get Tamil to work with a generic approach, I guess most of the edge cases for Myanmar would be covered by that as well. (Edit: seems like Tamil only has at most one diacritic, so it would have to be more general for Myanmar still.)