Solution
01) Sign up to cloudflare
02) Set these cname rules:
mydomain.com > appname-username.rhcloud.com (this will utilise ‘cname flattening‘)
www > mydomain.com
03) Set page rules:
http://www.mydomain.com/* > http://mydomain.com/$1
04) Set alias in OpenShift to mydomain.com
05) Make sure GoDaddy DNS record doesn’t have any conflicting cname or A record set up.
06) Let it simmer overnight and all of the original desired behaviour should be working.