Hold OPAMP Integrator at zero voltage (Guarantee defined slew rate)
This is a little crude, but I think it does what you are asking (sorry for the screen grab but links from the schematic editor are not working for me right now)



R2 and R3 bias Q1 so it turns on when the emitter is near 0V. They're not optimized and the turn-on will vary with temperature. 

If you want something much more precise, consider a comparator driving an analog switch across C1.