It is possible updating with the version 2.0.1. Here is the procedure:
1)
Download weasis-portable.zip and weasis.war.
2) Extract weasis-portable.zip to OsiriX.app/Contents/Resources/weasis (Erase the content of the weasis directory before extracting)
3) Unzip weasis.war and copy "resources.zip" and "substance.jnlp" into OsiriX.app/Contents/Resources/weasis/weasis.
Applying this modification with Osirix 5.9 will not allow to restart the application because of code signing issue. I think it is necessary to recompile Osirix without code siging.