forward DNS mapping to another NS address pool

I have been given a request to add a forward DNS mapping. The IP address
is for an IP pool not controlled by ourselves and no forward address has
been created by the authoritive nameserver. Strangely only a reverse and
now their is a need for a forward address.

This is what was suggested for our zone file

name IN A address from other ISP address pool not Authotive Name
Server for

I'm not in contact with the other ISP and so it would be nice if I could
sort it all out my end, but my understanding is that they need to give
it a name to which I alias. I.E they are the daddy, while my side is
just a link

so the record in my zone file would be

name IN CNAME name.domainname

But an evil shadow of doubt has come to my mind telling me that in my
ignorance their may be another way. Please can someone give me an
authoritive answer.

Kind Regards