We currently dont offer the possibility to signup to the OpenShift Express PaaS. We only offer a link to the signup page on OpenShift. The REST service now offers this capability and it's now up to us to include this into our client.
There are implementation details to discuss with the OpenShift Express team, since they currently offer this capability only with a shared secret (see Appcelerator and mails discussing this topic). As opensource project it's not possible for us to require a shared secret we have to hide from the public.