1. There is nothing else he is supposed to do. All those solutions were rightly advised by other repliers herein, he should have thought before marrying second time in a subsisting marriage all these and religion change now is also not a legal solution at all as it is done before marriage and second till forth marriages in leading life in same religion or post religion change is always with consent of first wife even in Indian Muslims.
2. What will be done may be done by one of his wife on whispers of society till that time he can juggle his day-night shift stories by keeping respective wives at a distance from each other’s localities – touch / contacts. In metros it is possible as the size of large metros makes two feline contenders for common space not see each others face so soon is remote.
3. For gossip mongers I doubt neighbor knowing one wife in one locality will also know another wife in another locality and even be it so he cannot escape such snooping unless he changes one wife’s city on plea of some fictitious job relocation grounds and ½ time in a month he spent in one city and rest time in another city citing ‘traveling nature’ of such relocated job.
4. If any case comes on floor of Court all he can plead is ‘plea bargaining’ wherein lesser compensation – lesser punishment if proved may get awarded to him that also based on showing good conduct to respective families he supported just before case went to floor of the Court and issues with respective minors welfare, thus ask him to keep evidences of money or such family expenses spent in safe place respectively; Courts have normally allowed on compassionate grounds plea bargaining in reference to fact but then compensation amount to left over second wife – minor child from that wife becomes higher as is seen in majority of cases and is all what may happen as if it is meant to happen, no point pondering now in great depth, that time he has already crossed. People should think deep before such crime of passion are committed not after such crime of passion is dispensed with and seek remedy and thus seek legal brains out for some remedy………
5. I am aware you are looking for that ‘perfect solution’ for your alleged to be friend, well, there is none in Law as two factors comes into play; society for which laws are there and law which follows society. If perfect solution which you are searching here and call it as single option to be given then ask your friend to divorce with good compensation to one of his love interest which in social milieu such bigamous personalities rarely do but then society always had its unique examples and ask him now to lead one such example from front? Will he and/or the larger social question now is will you tell him to do so? My Re. 1 bet – YOU SHOULD!
6. Hence I suggest you who by now know lots of insight from these replies and thus suggested to donot ask more questions on morality issues which are brushing social laws and are anyhow very very personal in nature and controversial too from each repliers point of view, as such issues are resting on fine balance between a persons morality or how society takes it all as to which he inhabits and only he should find a solution to his bigamous issues and a directional hints may be given as he is now not a minor person is my final stand as in public forums such questions may not be encouraged to such discussion depths.