Not exactly what you want, but when an infected player dies in versus, when he enters ghost mode the ghost_respawn_time event is fired, which contains his respawn time. But of course the event is only fired once and you won't be able to modify the time with the event.
CTerrorPlayer has a m_ghostSpawnClockCurrentDelay netprop. Might be what you want, but I'm just looking through a netprops dump and haven't tried anything with it. There's also m_isGhost, m_ghostSpawnClockMaxDelay, and m_ghostSpawnState.