Ok. Here is what I did, to solve the problem.
because my REngine is a singleton i was able to perform those R-Expressions, after the creation:
re.eval("log<-file('"+filepath+"')");
re.eval("sink(log, append=TRUE)");
re.eval("sink(log, append=TRUE, type='message')");
this codes writes every R-Output into the file specified by the String filepath. For non-singletons i would recommend to extend the REngine...