Question for the folks that want this - is there a reason that an action with *only* a due date wouldn't work? Most of my repeating "get it done by <some date>, but I don't care when" actions get entered that way.
Effectively, that's a "start as soon as possible, due by <date>" action. Admittedly, you can't hide an action like that from the Available list, but it's a heck of a lot less work. :-)
Assuming the answer is no, I'll see if I can hack something together this afternoon, but I can't make any promises.