It is shown that the infinitesimal flux tube model for a flux line, or fluxon, can yield an analytical result for the phase shift suffered by the electron beam in an electron holography experiment in a transmission electron microscope even when the specimen and the fluxon are tilted with respect to the optic axis so that the phase shift results from the contributions of the internal and external fields. By a suitable superposition of an ensemble of these elementary solutions it is possible lo investigate more realistic models for the fluxon core topography, like that introduced by London. The predicted amplified contour maps are calculated and their dependence on the specimen tilt and on the ratio between specimen thickness and London penetration depth is investigated. This new set-up gives detectable effects for the observation of fluxons by means of holographic methods and hence offers an alternative and perhaps more promising perspective for the success of such experiments with respect to the standard set-ups investigated in previous work.