Thermoelectric Generator Schematic
Put a high-power fixed-voltage shunt in parallel with the TEG.  I'd set it to let the voltage rise to 50 or 55V -- that should protect your LM2576HV, and still give you headroom above the TEG's maximum power point of 48V.  Then let the LM2576HV do its thing.  If you use the right value for your stack of Zeners, the shunt should stop conducting before the voltage gets down to 50V.  You could even put an LED in series with the Zeners as a rough indication that you're almost sucking the TEG dry.
Mind your volts and watts -- 96V can be fatal, and all the bits in the circuit below, except for R1, will dissipate considerable power.  So don't burn yourself, or kill yourself.  If you're not already accustomed to proper safety measures, learn.  This is house-wiring voltages, so there should be resources from DIY sites if nothing else.
Note that your shunt will have to dissipate up to 15W -- I'd design the thing for 20, in high heat.



simulate this circuit &ndash; Schematic created using CircuitLab