Not certain what you are looking for and how it would be benefical.
Currently you can use the KEY(nn, KEY=x$:x1$:x2$) to generate the key, also you can use the KGN function to generate the key based on the record contents.
Also you can specify more key fields than needed. For example if writing a generic access routine simply code it as KEY(nn,KEY=arg(K$,1,sep):arg(k$,2,sep):arg(K$,3,sep) ...