I've heard of people combining the two religions together. Witchvox.com usually has a few articles at a time about the subject. I know that many Christians all over the world have practiced witchcraft while holding their Christian beliefs, but using witchcraft (which is a tool/technique, not a religion itself) and believing in pagan tenants are different.
For me, the combination of the Christian belief and the Pagan belief is too difficult to work out. Pagan beliefs could make it work, but Christian beliefs condemn Pagan ones all around.
Many Pagans would say to a Christian-Wiccan or, as you call it, a Christo-Pagan (I like that term, rolls off of the tongue) that they are just holding onto their old Christian beliefs in fear, and that they need to make a decision on their beliefs one way or another. I remember when I "came home" to Paganism, I was scared to shake off the Catholicism I was raised with. I held fast to Mary (admittedly, not so fast to Jesus,... I dropped him almost instantly), and did alot of research. I went from Mary, to Mary of Magdalene, to Sophia, and outward and onward. Eventually, I shook off Christianity as something that was there, another facet of the great big jewel that is The Ultimate, but something that I generally don't agree with, nor enjoy.
I'm not saying that other people can't enjoy practicing Pagan and Christian beliefs together, but for me, after doing the research, reading the bible, taking the classes, I find that the two don't really mix, and I was much happier picking one.