It has worked for me before (with some small caveats), if you use the holdout LOP, connect its second output to the second input of the karmarendersettings lop in question and then hook on the "Import render vars from second input" on the Image Output - AOVs tab of the karmarendersettings.
*Edit: "Before" as in: earlier today, on build .387
Hi! Thanks for the tip. What do you mean by "Holdout LOP"? I've done a search for Holdout in Lops but I'm not finding anything.
Thanks for any help!