I've inquired about this with KLM in the past as I had a friend with a few thousand miles that they weren't going to use but wanted to give to me.
I was informed by KLM that miles are not transferable from one account to another, and as quoted above, cannot be earned for miles flown by anyone other than the actual member.
They do have a scheme where you can donate unwanted miles to their charity which uses them towards flights for sick children. I appreciate that's different to what you were asking, but figured would included it here for information in case anyone was wondering.