How to set IBM MQ specific headers to Camel exchange header so they can be forwarded back to MQ

Issue

I have a Camel route that gets a message from IBM MQ and after transformation writes it back to MQ.
I want to set the IBM MQ CCSID in the MQMD header of a message by using the IBM JMS properties described in

http://www-01.ibm.com/support/knowledgecenter/SSFKSJ_7.1.0/com.ibm.mq.doc/jm41050_.htm

i.e.
JMS_IBM_MQMD_CodedCharSetId
and
JMS_IBM_MQMD_Encoding

but apparently these properties are ignored if I set them in the exchange.getIn() header.