Somthing like that should be possible code and details might vary...
lang=python
import mitk.plugin
import mitk.ioutil
nodes = mitk.plugin.get_current_selection()
for node in nodes:
file_name = node.get_name()+'.nrrd'
mitk.ioutil.save(node.get_data(), file_name)
#exedo my pretty stuff an generate results
newNode = mitk.core.DataNode()
newNode.data = resultData
newNode.name = 'myCoolPyNode'
newNode.properties['coolProp'] = 'value'
datastorage.add_node(newNode, parents=[node])
Result: data of all selected nodes are saved.