You can create single association (link mapping) and provide label text using
your custom (java-) ParserProvider + constraint this association to be able
to connect only instances of different metaclasses (A with B, B with C, ...)
using OCL/java constraint.
Or you can create a number of associations (link mappings) connecting different
source/target metaclasses and having different labels. As a result you'll
have a lot of link mappings in .gmfmap model, but you will save time on writing
java code + plugging it into GMF-generated editor.