How to remove the session header set automatically by the REST plugin

Currently the REST plugin automatically adds the session key to the request in case one is already requested earlier. Rest server in my case exposes a separate api say "getSessionKey to request for the session key and the same is valid for only 30 mins.

Once the session key gets expired the api expect the session header not to be there as part of the subsequent call.

So the requirement is to remove the session header from the call. I checked the RESTHost api but there is no removeHeader api available. Can someone suggest how to remove the header from the REST request?

Thanks in advance,

Salil