We've already got a new client supporting the secure logins (and a bunch of other neat features), written by Rocon Software. (That was fast!) Find it here.
Meanwhile, I've been sitting on a 220 line patch to add StaticCling support to ez-ipupdate, a popular open source updater. Other projects use ez-ipupdate as a backend for their own dynamic dns support (such as M0n0wall) - so getting embedded StaticCling support would be great. Unfortunatley, the ez-ipupdate maintainer seems to have dropped off the planet. Anyone out there know how to get ahold of this guy? :)