I'm sure you could get the E175 several thousand feet above the published numbers fairly easily, to say nothing of using your technique ExAB. However, I'm not much for operating an aircraft outside of what its manufacturer says its capable of. I know Embraer's max altitude capability tables are conservative and I could safely go higher...but how much higher? At some point you enter test pilot territory a la PCL3901. I'll gladly burn the extra fuel to stay within established limits until Embraer puts out other numbers.