How do I set up reverse DNS?

There are three ways to accomplish this:

1) Ask your ISP to add the PTR records for you. In all likelyhood they are authoritative for the ip's DNS.

2) Ask your ISP to delegate the DNS, for the PTR records, to the widge name servers and add the PTR records.
ex: host:www type:PTR val:1.2.3.4 (on the widge zone update screen)

3) Set up classless subnet delegation, ask your ISP to add a CNAME record to their DNS for each PTR record. Then add the PTR records to the widge.
ex: www.example.com with an ip of 1.2.3.4
4.3.2.1.in-addr.arpa. IN CNAME 1.2.3.4.example.com (at the ISP)
host:www type:PTR val:1.2.3.4,1.2.3.4.example.com (on the widge zone update screen)
note that the CNAME record must match the data after the comma in the val text box

see What is classless subnet delegation?