Finally worked this out from the docs and some help from the Rackspace crew.
Importantly, for CDN enabled containers containing only CDN files, there is no point adjusting the container's meta-headers. These are only inherited by files not on the CDN.
I had to adjust the response headers on the font files themselves. Unfortunately this is only currently supported through the API and I used curl from the command line in Windows 7.
Authenticating
RACKSPACE DOCS
First step is to authenticate:
curl -d "{\"auth\":{\"RAX-KSKEY:apiKeyCredentials\":{\"username\":\"my_username\",\"apiKey\":\"my_api_key\"}}}" -H "Content-Type: application/json" "https://identity.api.rackspacecloud.com/v2.0/tokens"
Then extract the id of the token from the response and the publicURL of the endpoint related to cloudFiles. I copied the response to Notepad++ and searched for token and cloudfiles respectively.
Adjusting file response headers
RACKSPACE DOCS
I tried adjusting the headers with the following command:
curl -i -XPOST -H "x-auth-token: my-auth-token" -H "Access-Control-Expose-Headers: Access-Control-Allow-Origin" -H "Access-Control-Allow-Origin: *" https://storage101.lon3.clouddrive.com/v1/MossoCloudFS_my-end-point/container/pseudo-dir1/psuedo-dir2/my-site-icons.ttf
Did it work?
I got a HTTP/1.1 2xx response and checked it worked with:
curl -i -XGET -H "X-Auth-Token: my-auth-token" https://storage101.lon3.clouddrive.com/v1/MossoCloudFS_my-end-point/container/pseudo-dir1/psuedo-dir2/my-site-icons.ttf
Unfortunately you have to wait for the file's TTL to expire, or purge it to see a live result. When I did this it was taking over a day to do an edge purge. I checked the live version with:
curl -i -XGET https://live-version-container-hash.ssl.cf3.rackcdn.com/pseudo-dir1/psuedo-dir2/my-site-icons.ttf
Setting file response headers on upload
I settled on adding a version to my file and adding the headers during the upload:
curl -i -XPUT -H "x-auth-token: my-auth-token" -H "Access-Control-Expose-Headers: Access-Control-Allow-Origin" -H "Access-Control-Allow-Origin: *" https://storage101.lon3.clouddrive.com/v1/MossoCloudFS_my-end-point/container/pseudo-dir1/psuedo-dir2/my-site-icons1.0.0.ttf -T my-site-icons.tff
Performed from my local directory where the file my-site-icons.tff was located