What is the difference between an op-amp and a comparator? Look at the output capabilities. How can you make a comparator output act more like an op-amp's?
Things to think about for both.
1)Stability.
2)Input offset
2)CMR.
3)Output structure.
4)Driving logic gate.
5)Differential voltage range.
6)Common mode voltage range.
7)Speed / Bandwidth
Some hints for your answer may be gleaned from Analog Devices AN-849 "Using Op Amps as Comparators" http://www.analog.com/static/imported-files/application_notes/AN-849.pdf but the most important consideration may be that comparators are not intended for negative feedback operation so have not been internally compensated nor provisions made for external compensation. What does that mean? Also, a comparator is meant to provide a logic signal, so it has not been designed with a linear output stage. What are the implications of that?