This would be one of those things that require EXTENSIVE work and researching. As far as I know, it hasnt been done, its possible, but unless someone has some real good experience..there wont be much help. Id be interested in the same thing, but...cost of the cells and charging it seems to be an issue...(now..if they could only power it w/ gasoline..might be more efficient)..just thinking out loud. But hopefully if we can find one it can be experimented with.
I did a little reading and here is what I found...
Fuel cells are not legal for use on vehicles operated on public roads. I don't think there is any company that makes one that is approved for on-highway use by the Department Of Transportation. If your state has smog inspections, your car will not pass if there is a racing fuel cell installed. Also, if caught by a cop that knows anything you could easily get a ticket.
Just fyi
With that said... I would like to put one in my car in addition to the stock tank in order to have two different fuel options.