Reverse DNS to a Router??

[Pmann]

I have a client on a DSL line trying to download 128-bit encrypted software.
He gets an error from their server "The following error occurred during
Reverse DNS Lookup: host information not found".  He does not have a
registered domain name, only a DSL router at his site.  The router has an IP
address from a sub-netted Class C  that was given to me by my upstream ISP.
How would I create a reverse DNS record without a domain name to point to,
and should that record be created by the upstream who owns the Class C?

TIA
Peter
OLSI
www.olsi.com