You can define environment variables and use the Env tag as a placeholder.
<New id="dsDatasource" class="org.eclipse.jetty.plus.jndi.Resource">
<Arg>jdbc/dsProtWb</Arg>
<Arg>
<New class="org.apache.commons.dbcp.BasicDataSource">
<Set name="driverClassName">net.sourceforge.jtds.jdbc.Driver</Set>
<Set name='url'>jdbc:jtds:sqlserver://ROPFDN812Q:4900/dlmp_proteomics_wb_dev;instance=FDNDEV18;domain=mfad</Set>
<Set name="username"><Env name="LANID"/></Set>
<Set name="password"><Env name="LANPW"/></Set>
</New>
</Arg>
</New>