It is true that you can not get child support from the current wife of the ex husband.
It is also true that I have seen some head turning results in a divorce court.
If you are very serious about this avenue, then if I were you I would retain a very aggressive divorce attorney and also a very aggressive private investigator.
Child support is not black-and-white based on what the current income of the parent is today, but is in fact based on what the earnings potential of that parent is. Just for an example, if Richie Rich founder of a famous software company, richest man in America were unemployed today, the court would not be bound to accept today's earnings with regard to a basis for child support. Even in the present economy I have observed judges tell father's to actively seek employment and come back in two weeks to report either that they have a job or what they have done to obtain employment.
It is also true that you have the burden of proof here and a difficult battle. But, your question should not be can you get support from the current wife of the X. Your goal should be to prove that (a) he has an earnings capacity that even in the current economy he is not making best efforts to optimize, and (b) wifey is giving him support. A nice investigative video of him at a fine yacht club, golf course or other posh setting with wifey's money would be worth a thousand words.
If you want to be aggressive and spend a few buck, then ask the question differently and you may get the result you want.
Sorry guys, in this instance, I do not think that answering the question as posed helped the cause of the individual.
This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.