Is there any way to get sbt (0.10) to declare a jar at some URL (http://foo.com/bar-1.1.jar) as a library dependency?
You can specify an explicit url for a jar. If you use the basic configuration just include it like follows
libraryDependencies += "slinky" % "slinky" % "2.1" from "http://slinky2.googlecode.com/svn/artifacts/2.1/slinky.jar"
As stated in the sbt wiki on GitHub the url is used as a fallback in case the artifact isn't resolved via ivy. For more details see paragraph Explicit URL