Can this scheme give a wideband phase shift?
One way to do a wideband phase shift is to do an FFT to amplitude/angle in the frequency domain, add something to all the angle points, and then do an inverse FFT back into time domain. That will require lots of processing power, although a dsPIC might be able to do it for audio. A high end dsp chip will definitely be able to handle it for audio. You also might be able to do it with a PC, although there will be some latency there.
Regards, Bob Monsen