I am looking forward to study Islamey in a while. Like 2 years or so. ...
The closest I can think of as a pre-requisite would be Liapunov's transcendental etude Op. 11 No. 10 (Lezghinka), which is also quite difficult but I think more manageable than Islamey. It was modeled after Islamey and you'll really hear the similarities between the two. And honestly, after learning Lezghinka I'm not sure I'll even bother learning Islamey because in many ways I prefer Liapunov's piece. It's very fun, a huge crowd pleaser, and rarely performed. Win win win.
Why not learn some of his better works first? B-flat minor sonata, b-minor scherzo and one of his transcriptions...You might then realize that Islamey really isn't worth the trouble