Additional settings have been added under the Advanced tab on tunnel detail pages to support chaining IP updates.
Users of the Dynamic DNS feature of dns.he.net can now just use the tunnelbroker endpoint update API to also update a single hostname with dns.he.net to the same IPv4 address. Simply enter in the hostname and API key associated with updates to that hostname on the detail page for the associated tunnel, and the next time you successfully update your endpoint with https://tunnelbroker.net/nic/update using the Dyn-compatible API, the dns.he.net record will update. You can check update status and refresh updates if needed on the tunnel detail page.
Do note, errors updating dns.he.net records are not returned to the tunnelbroker updater as those updates push after the tunnel updater is finished.
UPDATE - Since I see many people trying... This addition only works with domains hosted with DNS.HE.NET and with a dynamic update key associated with it. This does not try to update anything hosted with DynDNS, EasyDNS, or any other DNS service.