Oye conejita linda -- yes, check out any of the tour operators in either Leon or Chinandega. Your best bet is probably QuetzalTrekkers, a Guatemala-based NGO that set up a shop in Nicaragua, in Leon, a few years ago and offers lots of overnight volcano excursions. Here's what they offer for Cosiguina:
http://www.quetzaltrekkers.com/niccosig.htmlOh yeah, profits go to help street kids.