Our committee talked over your email and Cindi Laurent (Vice Chair) gave these suggestions:
Use the UEB ligature symbol for the undertie - dots 45, 235 - and do a TN to explain that it is under the word in print and replaces the print hyphen if there is one.
For the letters above the tie, I would suggest putting them in parentheses and placing them after the 2nd letter of the tie (so for quan<b>d e</b>lle you would have q u a n bold symbol d ligature bold symbol e open paren t close paren lle). It's ugly, but it's all there. You would also need a TN to explain that the letters that appear above the tie are enclosed in parens and follow the tied letters. I'd probably omit the bold as I think it's just showing that those sounds are tied together and the ligature does that (in my opinion). And, of course, this suggestion is completely based on the the small snippet of the book we can see.
I like the 26, 35 one better, myself. Having done quite a few French books, it's closer to the intent of the liaison symbol I learned in school. Also cleaner. I would probably have put the single letters on the line above. The question Jill posted was originally mine and that liaison keeps popping into my head. I used Patrick's suggestion but it went against the grain.