There was a point in the Death and Return of Bruce Waye that tied into some random ass Riddler story I read as a kid when I had a subscription to Batman and I was like "holy shit! I remember that story! that weird flash back stuff was so weird!" and somehow he tied that shit in 20+ years later and it made sense. I realize that the appeal of something like this is super fucking low though so I can see why not many people would like it, but I enjoyed it.
Everything of his run dating back to Batman and Son, through RIP, the Death and Return into Batman Inc. is this. The Batmen of Other Nations, Dr. Hurt's experiment, Batman of Zur-En-Arrh, etc. all come from those old comics. The Black Casebook tpb collects a ton of them* and Morrison wrote a lucid few pages essay about it and how it creates the groundwork for RIP.
His core idea was that all this insane stuff that Batman comics dismissed for years, should be canon and can be explained in realistic ways and that considering everything Batman has experienced in the Justice League and beyond his world shouldn't be entirely rational, hence The Black Casebook which is where he puts all the shit that makes no sense that he someday hopes to find an explanation for.
EDIT: I actually had familiarity with a lot of these stories because I had a number of 1960's Batman comic books from the old "random bags of comics" you'd get at conventions/stores for like a buck or two. Also had the The Greatest Batman Stories Ever Told series which had a number of them.
EDIT2: From the I Hate Grant Morrison blog:
Bruce and Alfred talk about "The Black Casebook," which they might as well say "hey you know that thing we've never mentioned? Yeah that." More like Batman and the Deathly Hallows. The Black Casebook is a record Batman has been keeping of all the unexplained phenomena that has ever happened (within it probably lies the reason DC hired and kept Grant Morrison around). Coincidentally, Alfred had just completed transferring the Black Casebook to a memory stick (the Black Memory Stick just doesn't have the same ring to it). When it comes to data management and going green, Alfred is on top of it!
*
"A Partner For Batman" from Batman #65
"Batman - Indian Chief" from Batman #86
"The Batmen of All Nations" from Detective Comics #215
"The First Batman" from Detective Comics #235
"The Club of Heroes" from World's Finest Comics #89
"The Man Who Ended Batman's Career" from Detective Comics #247
"Am I Really Batman?" from Batman #112
"Batman - The Superman of Planet X" from Batman #113
"Batman Meets Bat-Mite" from Detective Comics #267
"The Rainbow Creature" from Batman #134
"Robin Dies At Dawn" from Batman #156
"The Batman Creature" from Batman #162