User blog comment:Vivaporius/AT Idea: Imperial Civil War/@comment-4051689-20120412190626/@comment-2253300-20120425182631

Firstly It could be done with an appropriately powerful Psyker, as their minds are linked to the Warp and that connection could sustain a Daemon. Secondly, and this is just speculation on my part from what I have seen in canon. it seems that Daemon Princes don't necessarily play by the same rules as other Daemons. Daemon Princes routinely lead CSM Warbands, and if they were unable to remain within Real Space for an extended length then this would not be possible. An example that comes to mind is Kernax Voldorius. A Daemon Prince that lead an Alpha Legion Warband. He was the subject of an extended hunt executed by the White Scars' Master of the Hunt, Kor'sarro Khan. Kor'sarro would have not had a chance to track his prey if he were in the Warp. He would have had to remain in Real Space for an extended amount of time. The reason for this exception to the Daemon rule is most likely the mortal origins of the Daemon Princes.