hmmm.... perhaps finding a charity run by the church or by Christians?
something like:
www.love-link.org (run by a Christian couple) or
www.hogarvitoguarato.org/fhp/indexen.asp (funded by Father Vito Guarato, of the Franciscan order)
Perhaps not exactly this ones, but something like that in the US? while it isn't exactly tithing, it IS giving money to the work of God through members of the church...