Echo Tomography is a powerful technique which enables us to probe the accretion geometry in active LMXBs by studying reprocessing of X-rays into UV/optical radiation. If reprocessing takes place in the companion star, time delay as a function of the orbital phase can yield accurate dynamical masses. Previous attempts, using broad band photometry, have shown instead that the accretion disc is the dominant reprocessing site in the continuum. However, we have shown that Bowen fluorescence lines in Sco X-1 are extremely efficient diagnostics of reprocessing in the companion star. We propose to obtain 72 Ks observations of Sco X-1, simultaneous to Bowen blend lightcurves, to echo-map the irradiation of the companion star in Sco X-1 and obtain accurate system parameters.