textproc/xalan-c with textproc/xerces-c3

[O. Hartmann]

For some important scientific software provided by NASA, ESA and JPL, I 
need xerces-c3 library on my system. But there is always a conflict with 
textproc/xalan-c, which requires textproc/xerces-c2. Xerces-c3 and 
Xerces-c2 seem to install files at the same place, even the libraries 
and shortcut-links to the libraries.

Is there a solution having either both textproc/xerces-c2 and xerces-c3 
installed or textproc/xalan-c using xerces-c2 OR xerces-c3?

Oliver