I guess the closest we can come to is to find a trigger, even if it's a good one, to them... they probaby just think of them as strong memories...but it's a start... once you have them in that frame of mind (sensing with all their senses if they can, of something long ago..) see if you can get them to find something not enjoyable to fully remember.

I agree, telling them doesn't make any difference. They won't get it.