It certainly would be possible to carb using it, but I'd be a bit leery about doing that. It seems like that would be an easy way to under or over carb your beers.
Personally I think your best bet would be to add the juice right after flame-out, or if you use a secondary, toss it in there before you rack. It will ferment the sugars, but should leave you with plenty of cherry taste. The best way to get more taste would be to add more I suppose.