Isn't the proximity effect a delocalization of the condensate outside the superconductor ? Then, one can probe this effect via tunnelling (density of state probe).
Vortex are also an inhomogeneity of the condensate that one can easily visualise (STM, X-ray, ...).
Well, any kind of inhomogeneity can be seen as I believe. But I do not know of an experiment probing the stable, constant condensate (each time, one needs phase gradient in what I know).
It may also be possible to probe the edge currents proposed by London long ago (I'm not aware of such a detection, nor of an actual experiment).
EDIT: Ok, an other way of answering, I may have misunderstood the question. After reading this topic, maybe some better answers would be:
1) The coupling of two electrons to form a bound state, mediated by a phonon (à la Cooper / Bardeen and Schrieffer). So in principle one could generate it by phonon excitations (already done in the 70's if I remember correctly)
2) The emergence of a macroscopic quantum state from interacting electrons, and the creation of a quantum macroscopic state with all electrons sharing the same phase. So in principle one could observe the growing of the phase rigidity.
3) The emergence of a gapped excitation at the Fermi level.
But I still believe the question is not clear ... :-(
Well, as it must at the beginning of organising minds :-)