Hi There,
That would be possible
You need to create the alphabet using <a> and give an Id to each section.
So for example it would something like this <a href="#a">(A)</a><a href="#b">(B)</a><a href="#c">(C)</a> and so on.
You will add this code in a raw element or text element in Cornerstone.
Than you need to go to the sections you want to link them to for example section A and give the ID: a on the ID BOX and so on.
Hope that helps,
Joao