Jim Oberg says that it’s possible. It’s certainly technically doable, and a cool idea. The big question, I think, is the market at the price that it’s doable for. As they point out, though, it’s certainly within the capability of many governments to do it, if they just want the prestige. I’m not sure that it could be justified scientifically. Unfortunately, the Soyuz capsule is too small to fit someone like this.

[Disclosure: I’ve done some consulting for Constellation Services in the past, and may in the future, but I was previously unaware of this.]