slapo-memberof(5) does not support tool mode; in order to populate the memberOf attribute of an existing database you need to use ldapadd(1). You could, for example, dump your group entries, remove them, and re-add them via ldapadd(1).
Hi Ando, correct me if I'm wrong, but another method is to populate a slave with syncrepl. slapo-memberOf should be triggered in this case too, isn't it?
Thanks Marco