Can attorney holder depose for the complainant in complaint u/s 420 ipc?

Section 256 under the CrPC clarifies if the complainant does not appear on the date of hearing in the court, the magistrate shall in most likeliness acquit the accused, provided that the complainant is not represented by a pleader or the magistrate feels that the personal attendence of the complainant couldn't have been done away with.

So, I don't think you should be facing any problems, however, I would advise you to inform/take prior permission from the magistrate.  

To depose means to testify under oath, its like becoming witness in place of someone. No body can depose for any natural person. The issue regarding attorney holder has to be understood in right perspective. If attorney holder had attorney in his name for the transaction involved and subsequently got cheated then he can give evidence and he can become complainant too by giving the name of the principle person who granted him the attorney. Its not that someone gives a GPA to some xyz and asks him to go depose.