Heh, no need to wait for 1.5, I've already added this feature
It's done and tested, I just need to finish adding the instructions to the manual, then create some kind of demo GIF to go with the patch (and build the actual patch for release, of course
).
Took me all afternoon to finish, but worth it. Half that time was spent getting it to be compatible with the preview system, which was never meant to work with more than one layer at a time so it took a lot of consideration to figure out how best to include this so that you could see the results dynamically.
Will be out soonish, although it's already late tonight so I don't really have time to do the rest of the work now...