During the TESS prime mission, 74% of the sky area will only have an observational baseline of 27 days. For planets with orbital periods longer than 13.5 days, TESS can only capture one or two transits, and the planet ephemerides will be difficult to determine from TESS data alone. Follow-up observations of transits of these candidates will require precise ephemerides. We explore the use of existing ground-based wide-field photometric surveys to constrain the ephemerides of the TESS single-transit candidates, with a focus on the Kilodegree Extremely Little Telescope (KELT) survey. We insert simulated TESS-detected single transits into KELT light curves, and evaluate how well their orbital periods can be recovered. We find that KELT photometry can be used to confirm ephemerides with high accuracy for planets of Saturn size or larger with orbital periods as long as a year, and therefore span a wide range of planet equilibrium temperatures. In a large fraction of the sky we recover 30% to 50% of warm Jupiter systems (planet radius of 0.9 to 1.1 R_J and 13.5 < P < 50 days), 5% to 20% of temperate Jupiters (50 < P < 300 days), and 10% to 30% of warm Saturns (planet radius of 0.5 to 0.9 R_J and 13.5 < P < 50 days). The resulting ephemerides can be used for follow-up observations to confirm candidates as planets, eclipsing binaries, or other false positives, as well as to conduct detailed transit observations with facilities like JWST or HST.
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