Haven't heard of an undocumented API for this, and plans for new SDK functions don't tend to get discussed in advance.
As Rob has noted this request has been made in the feature request site so they know there is interest in it. You should vote for the feature if you want it and haven't already done so.
He has also posted a recipe as a workaround. Not a big fan of the keyboard stuffing approach myself - I have robustness and cross-platform compatibility concerns about it - but you might be happy to use it for your purposes.
Yeah, I have some good news and some bad news:
- Good news: Keyboard stuffing (as implemented in the elare framework) works equally well on both platforms, provided the appropriate keystroke exists on both platforms.
(Mac version uses applescript, Windows uses autohotkey - both assure Lightroom is the target) - Note: @2011-07-30, I haven't actually tested this particular function on Mac - but I've tested other similar functions on both platforms.
- Bad news: It doesn't always work on either platform, since keystrokes may be usurped by open dialog boxes and open text fields in Lightroom...
- Good news: failure is 100% detectable.
If the kludgy nature of this solution would be more bad than good for you and/or your users, then this is not a viable solution.
If your users would prefer the caveats in order to be able to get the job, then this solution will work well enough for now.
PS - I'm presently using it in ChangeManager and its a godsend for me. Since I understand the limitations, my failure rate is appx. 0%.