Just say, when asked or when appropriate: "I want to believe in Christianity, but I just can't. I'm working on it, as best I can."
And then make sure you do not attack, subvert or damage Christianity; but instead support Christianity by thought (including prayer) and word and deed.
My understanding of things (based mostly on Pascal, but also many other authorities whom I trust) is that such a person will attain salvation even if he never (in this life) actually gets to the point that he can say that he is a Christian.
Indeed, I would go further: Anyone who truly and sincerely wants to be a Christian, is from that moment onwards in effect a Christian.
Again: anyone who wants to be a Christian (and lives in accordance with that desire) is a Christian - in the strong sense that he can know for sure that he will become a Christian, in the fullness of time.
"Seek and ye shall find" Matthew 7: 7.
It is a promise.