I'm not sure this answers your question exactly, but in case it helps...
I'm able to keep my books on my MicroSD card and read them using Coolreader on my Samsung galaxy tab 2 7, running ICS.
To do that, I download the books to my MicroSD card, then, in the Coolreader book list, I navigate up to root, then down to the external SD card.
Once there, select "scan all books in directory" to add those books to Coolreader's list, so they show up in the "by author" "by series" "all books" lists. (You have to repeat that anytime you add more books.)
Note that in ICS, they label the internal memory/storage area as "sdcard", and label your microsd card as "extSDcard". They've also made it clunky for apps to interact with external SD cards in general, but that's a whole topic in itself.