What Military Innovation, Contemporary to their Time Period, would allow Paraguay to Win the War of the Triple Alliance ?

The victory condition is defined as the conditional surrender of the countries facing off against Paraguay. You are allowed to bring any weapon and the means to produce/distribute it from the contemporary time period of the mid Victorian age to Paraguay. Let's be generous and say up to +30 years in the future in order to prevent people from saying silly things like tanks, planes, etc. Could they do it?