A common method is to couple the AC signal through a capacitor. The DC level at the output of the cap can be shifted to whatever you want with a resistor to the desired bias voltage. The RC time constant of the capacitor and resistor has to be large enough to transfer the lowest AC frequency of interest, of course.
Recently i was engaged in making desired figures on cro.There also i needed dc shift in ac signal.I directly added ac & necessary dc voltage using resistors and this seem to work fine.