This question touches on the unique tragedy of Lolita. Nabokov possesses the incredible ability to create a sense of victimization to Humbert's character. He can essentially do this because of an incredible hold on language and an ability to write in such a way that we compartmentalize the brutality of Humbert. While Humbert creates a sense of victimhood over his character, he is by no means innocent. Rape, murder, and pedophilia are all parts of Humbert's character, but through Nabokov's command over language, we keep reading.

When I try to analyze my own cravings, motives, actions and so forth, I surrender to a sort of retrospective imagination which feeds the analytic faculty with boundless alternatives and which causes each visualized route to fork and re-fork without end in the maddeningly complex prospect of my past.

This is an example of the portrait of victimhood that Humbert attempts to present to the reader. This example shows Nabokov's belief that through language, we can ignore indiscretion and immorality.

My opinion is that Humbert is not the victim. There is no question that Lolita is the primary victim in this story, and there are many other victims in Lolita as well, such as Lolita's mother, Charlotte. Your question touches on the theme of the entire novel: what behaviors and which victims will we ignore when the words are depicted so beautifully before us?

This is an intriguing question.  For your purposes, treating Humbert as the victim of his perverse nature and ideas may be easier as you may be better able to find more "evidence" to support this thesis.  For, he seems more driven by his nature, driven to devise a way to be near the girl by marrying the mother, yet it is Lolita who initiates the lovemaking at the motel.  Later, in Chapter 19 Humbert reflects, "I have often wondered why she did not go for ever that day.... Was it some unripe particle in some general plan?"  It seems at times that Humbert feels a sense of fate in his relationship with Lolita.