[curt.clifton]

Originally Posted by johnrover

Actually - I'm mistaken. Curt's script adds a task using the highlighted message, not the incoming message. Therefore rule integration doesn't quite work. I'm not applescripter – can anyone advise on this

From Apple Mail help:

When Mail invokes an AppleScript as a rule action, it looks for a handler named "perform mail action with messages," which receives a list of messages as its direct object, with an optional parameter that specifies the rule being executed. Once you have the rule object and the list of messages, you can access all the properties that are shown in Mail's AppleScript dictionary for these objects.

So it should be straightforward to create a script that creates actions for every matched rule. I've added creating such a script to my "Migrate to OmniFocus" project, but if someone else created it first that would be great.