I was playing around and have achieved this.
Font is Times New Roman (which I don’t like much) 10.5pt, and is has the “real” superscripted characters “e” and “r”. All other fonts that I tried makes the “superscript” higher than the number.
So: Create this in your external text editor, copy and paste into the “custom text” property of repeat endings in Engrave mode.
As one can see, there are different spacing issues after the 1. and 2. The two first "er/e"s are attached directly to the number, the next two to a hard space after it.
It is a first attempt. Would it be acceptable to a discerning native French speaker/writer/singer, Marc?